Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2018	Nov. 05, 2018
Document And Entity Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3
Trading Symbol	CSTR
Entity Registrant Name	CAPSTAR FINANCIAL HOLDINGS, INC.
Entity Central Index Key	0001676479
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Voting
Document And Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		17,261,763
Nonvoting
Document And Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		132,561

Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Assets
Cash and due from banks	$ 8,563	$ 9,506
Interest-bearing deposits in financial institutions	41,279	68,572
Federal funds sold	2,747	4,719
Total cash and cash equivalents	52,589	82,797
Securities available-for-sale, at fair value	187,469	192,621
Securities held-to-maturity, fair value of $3,766, and $3,848 at September 30, 2018 and December 31, 2017, respectively	3,740	3,759
Loans held for sale	50,499	74,093
Loans	1,073,870	947,537
Less allowance for loan losses	(15,218)	(13,721)
Loans, net	1,058,652	933,816
Premises and equipment, net	9,584	5,884
Restricted equity securities	8,817	8,806
Accrued interest receivable	4,430	4,084
Goodwill	6,219	6,219
Core deposit intangible		23
Other assets	34,908	32,327
Total assets	1,416,907	1,344,429
Deposits:
Non-interest-bearing	239,792	301,742
Interest-bearing	307,299	274,681
Savings and money market accounts	376,985	367,246
Time	202,327	176,197
Total deposits	1,126,403	1,119,866
Federal Home Loan Bank advances	125,000	70,000
Other liabilities	7,994	7,617
Total liabilities	1,259,397	1,197,483
Shareholders’ equity:
Series A convertible preferred stock, $1 par value; 5,000,000 shares authorized; 878,049 shares issued and outstanding at September 30, 2018 and December 31, 2017	878	878
Additional paid-in capital	121,646	118,120
Retained earnings	28,741	18,892
Accumulated other comprehensive loss, net of income tax	(5,881)	(2,527)
Total shareholders’ equity	157,510	146,946
Total liabilities and shareholders’ equity	1,416,907	1,344,429
Voting
Shareholders’ equity:
Common stock	11,993	11,450
Nonvoting
Shareholders’ equity:
Common stock	$ 133	$ 133

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Securities held to maturity, fair value	$ 3,766	$ 3,848
Preferred stock, par value	$ 1	$ 1
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	878,049	878,049
Preferred stock, shares outstanding	878,049	878,049
Voting
Common stock, par value	$ 1	$ 1
Common stock, shares authorized	20,000,000	20,000,000
Common stock, shares issued	11,992,561	11,449,465
Common stock, shares outstanding	11,992,561	11,449,465
Nonvoting
Common stock, par value	$ 1	$ 1
Common stock, shares authorized	5,000,000	5,000,000
Common stock, shares issued	132,561	132,561
Common stock, shares outstanding	132,561	132,561

Consolidated Statements of Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Interest income:
Loans, including fees	$ 14,167	$ 12,095	$ 40,197	$ 33,935
Securities:
Taxable	951	838	2,775	2,827
Tax-exempt	248	304	784	944
Federal funds sold	17	7	56	26
Restricted equity securities	132	108	389	271
Interest-bearing deposits in financial institutions	267	169	679	387
Total interest income	15,782	13,521	44,880	38,390
Interest expense:
Interest-bearing deposits	1,146	635	2,793	1,839
Savings and money market accounts	1,409	772	3,827	2,360
Time deposits	985	706	2,468	1,750
Federal funds purchased	1	2	3	13
Federal Home Loan Bank advances	698	563	1,813	1,083
Total interest expense	4,239	2,678	10,904	7,045
Net interest income	11,543	10,843	33,976	31,345
Provision for loan losses	481	(195)	1,328	12,900
Net interest income after provision for loan losses	11,062	11,038	32,648	18,445
Noninterest income:
Net gain (loss) on sale of securities	(1)	9	2	42
Tri-Net fees	373	367	1,227	748
Other noninterest income	684	539	2,157	1,667
Total noninterest income	3,218	3,372	9,072	8,171
Noninterest expense:
Salaries and employee benefits	6,514	5,119	19,111	14,989
Data processing and software	803	709	2,411	2,040
Professional fees	255	336	1,074	1,050
Occupancy	544	531	1,600	1,518
Equipment	520	564	1,661	1,604
Regulatory fees	228	270	664	877
Merger related expenses	540		875
Other operating	666	946	2,259	2,988
Total noninterest expense	10,070	8,475	29,655	25,066
Income before income taxes	4,210	5,935	12,065	1,550
Income tax expense	554	1,516	1,702	141
Net income	$ 3,656	$ 4,419	$ 10,363	$ 1,409
Per share information:
Basic net income per share of common stock	$ 0.30	$ 0.39	$ 0.87	$ 0.13
Diluted net income per share of common stock	$ 0.28	$ 0.35	$ 0.79	$ 0.11
Weighted average shares outstanding:
Basic	12,040,229	11,279,364	11,851,476	11,239,093
Diluted	13,113,775	12,750,423	13,052,758	12,758,091
Treasury Management And Other Deposit Service Charges
Noninterest income:
Noninterest income:	$ 528	$ 427	$ 1,357	$ 1,097
Mortgage Banking Income
Noninterest income:
Noninterest income:	$ 1,634	$ 2,030	$ 4,329	$ 4,617

Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 3,656	$ 4,419	$ 10,363	$ 1,409
Unrealized gains (losses) on securities available-for-sale:
Unrealized holding gains (losses) arising during the period	(1,193)	526	(6,120)	2,433
Reclassification adjustment for (gains) losses included in net income	1	(9)	(2)	(42)
Tax effect	312	(198)	1,600	(915)
Net of tax	(880)	319	(4,522)	1,476
Unrealized losses on securities transferred to held-to-maturity:
Reclassification adjustment for losses included in net income		79	14	162
Tax effect		(30)	(4)	(62)
Net of tax		49	10	100
Unrealized gains (losses) on cash flow hedges:
Unrealized holding gains (losses) arising during the period	129	89	697	(123)
Reclassification adjustment for (gains) losses included in net income	224	159	698	472
Tax effect	(50)	(33)	(237)	47
Net of tax	303	215	1,158	396
Other comprehensive income (loss)	(577)	583	(3,354)	1,972
Comprehensive income	$ 3,079	$ 5,002	$ 7,009	$ 3,381

Consolidated Statements of Changes in Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Preferred Stock	Common Stock,Voting	Common Stock,Nonvoting	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss
Beginning balance at Dec. 31, 2016	$ 139,207	$ 878	$ 11,205		$ 116,143	$ 17,132	$ (6,151)
Beginning balance, shares at Dec. 31, 2016			11,204,515
Issuance of restricted common stock, net of forfeitures and withholdings to satisfy employee tax obligations	(264)		$ 21		(285)
Issuance of restricted common stock, net of forfeitures and withholdings to satisfy employee tax obligations, shares			21,480
Stock-based compensation expense	771				771
Excess tax benefit from stock compensation	644		$ 72		572
Excess tax benefit from stock compensation, shares			71,517
Exercise of common stock warrants	465		$ 49		416
Exercise of common stock warrants, shares			48,986
Net income	1,409					1,409
Other comprehensive income (loss)	1,972						1,972
Ending balance at Sep. 30, 2017	144,204	878	$ 11,347		117,617	18,541	(4,179)
Ending balance, shares at Sep. 30, 2017			11,346,498
Beginning balance at Dec. 31, 2017	146,946	878	$ 11,450	$ 133	118,120	18,892	(2,527)
Beginning balance, shares at Dec. 31, 2017			11,449,465	132,561
Issuance of restricted common stock, net of forfeitures and withholdings to satisfy employee tax obligations	(420)		$ 23		(443)
Issuance of restricted common stock, net of forfeitures and withholdings to satisfy employee tax obligations, shares			23,195
Stock-based compensation expense	940				940
Exercise of employee common stock options	$ 1,943		$ 334		1,609
Exercise of employee common stock options, shares	508,834		333,726
Exercise of common stock warrants	$ 1,606		$ 186		1,420
Exercise of common stock warrants, shares			186,175
Common and preferred stock dividends declared	(514)					(514)
Net income	10,363					10,363
Other comprehensive income (loss)	(3,354)						(3,354)
Ending balance at Sep. 30, 2018	$ 157,510	$ 878	$ 11,993	$ 133	$ 121,646	$ 28,741	$ (5,881)
Ending balance, shares at Sep. 30, 2018			11,992,561	132,561

Consolidated Statements of Cash Flows (Unaudited) - USD ($)	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities:
Net income	$ 10,363,000	$ 1,409,000
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for loan losses	1,328,000	12,900,000
Accretion of discounts on acquired loans and deferred fees	(948,000)	(537,000)
Depreciation and amortization	303,000	345,000
Net amortization of premiums on investment securities	803,000	984,000
Net gain on sale of securities	(2,000)	(42,000)
Tri-Net fees	(1,227,000)	(748,000)
Net gain on sale of loans	(6,000)	(67,000)
Net loss on disposal of premises and equipment		137,000
Stock-based compensation	940,000	771,000
Deferred income tax expense (benefit)	406,000	(445,000)
Origination of loans held for sale	(395,851,000)	(409,179,000)
Proceeds from loans held for sale	425,007,000	403,497,000
Net increase in accrued interest receivable and other assets	(1,974,000)	(1,320,000)
Net increase (decrease) in accrued interest payable and other liabilities	1,766,000	(2,630,000)
Net cash provided by operating activities	36,579,000	458,000
Activities in securities available-for-sale:
Purchases	(22,127,000)	(11,754,000)
Sales	5,778,000	34,299,000
Maturities, prepayments and calls	14,611,000	14,718,000
Activities in securities held-to-maturity:
Maturities, prepayments and calls		1,332,000
Purchase of restricted equity securities	(11,000)	(2,767,000)
Net increase in loans	(125,216,000)	(49,154,000)
Purchase of premises and equipment	(3,980,000)	(1,074,000)
Proceeds from the sale of premises and equipment		3,000
Net cash used in investing activities	(130,945,000)	(14,397,000)
Cash flows from financing activities:
Net increase (decrease) in deposits	6,537,000	(37,228,000)
Proceeds from Federal Home Loan Bank advances	110,000,000	135,000,000
Payments on Federal Home Loan Bank advances	(55,000,000)	(95,000,000)
Exercise of common stock options and warrants, net of repurchase of restricted shares	3,129,000	845,000
Common and preferred stock dividends paid	(508,000)
Net cash provided by financing activities	64,158,000	3,617,000
Net decrease in cash and cash equivalents	(30,208,000)	(10,322,000)
Cash and cash equivalents at beginning of period	82,797,000	80,111,000
Cash and cash equivalents at end of period	52,589,000	69,789,000
Supplemental disclosures of cash paid:
Interest paid	10,624,000	6,951,000
Income taxes	942,000	2,142,000
Supplemental disclosures of noncash transactions:
Loans charged off to the allowance for loan losses	251,000	12,369,000
Mortgage Banking Income
Adjustments to reconcile net income to net cash provided by operating activities:
Mortgage banking income	$ (4,329,000)	$ (4,617,000)

Summary of Significant Accounting Policies	9 Months Ended
Summary of Significant Accounting Policies	Sep. 30, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	NOTE 1 – SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Basis of Presentation The accompanying unaudited consolidated financial statements as of and for the period ended September 30, 2018 include CapStar Financial Holdings, Inc. and its wholly owned subsidiary, CapStar Bank (the “Bank”, together referred to as the “Company”). Significant intercompany transactions and accounts are eliminated in consolidation. The accompanying unaudited consolidated financial statements have been prepared in accordance with instructions to Form 10-Q and do not include all information and footnotes required by U.S. generally accepted accounting principles (“U.S. GAAP”) for complete financial statements. All adjustments consisting of normally recurring accruals that, in the opinion of management, are necessary for a fair presentation of the financial position and results of operations for the periods presented have been included. These unaudited consolidated financial statements should be read in conjunction with the Company’s consolidated financial statements and related notes appearing in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017. Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Material estimates that are particularly susceptible to significant change relate to the determination of the allowance for loan losses, determination of impairment of intangible assets, including goodwill, the valuation of our investment portfolio, deferred tax assets and estimated liabilities. There have been no significant changes to the Company’s critical accounting policies as disclosed in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017. Subsequent Events Accounting Standards Codification (“ASC”) 855, Subsequent Events, establishes general standards of accounting for and disclosure of events that occur after the balance sheet date but before financial statements are issued. The Company evaluated all events or transactions that occurred after September 30, 2018 through the date of the issued financial statements.

Securities

9 Months Ended

Sep. 30, 2018

Investments Debt And Equity Securities [Abstract]

Securities

NOTE 2 – SECURITIES

The amortized cost and fair value of securities available-for-sale and held-to-maturity at September 30, 2018 and December 31, 2017 are summarized as follows (dollars in thousands):

	September 30, 2018									December 31, 2017
	Amortized Cost		Gross unrealized gains		Gross unrealized (losses)			Estimated fair value		Amortized Cost		Gross unrealized gains		Gross unrealized (losses)			Estimated fair value
Securities available-for-sale:
U. S. government agency securities	$	11,054	$	—	$	(589	)	$	10,465	$	11,433	$	12	$	(168	)	$	11,277
State and municipal securities		45,738		228		(1,721	)		44,245		51,790		1,430		(222	)		52,998
Mortgage-backed securities		109,983		—		(4,781	)		105,202		108,236		40		(1,714	)		106,562
Asset-backed securities		15,687		26		—			15,713		16,575		—		(198	)		16,377
Other debt securities		11,868		26		(50	)		11,844		5,326		81		—			5,407
Total	$	194,330	$	280	$	(7,141	)	$	187,469	$	193,360	$	1,563	$	(2,302	)	$	192,621
Securities held-to-maturity:
State and municipal securities	$	3,740	$	31	$	(5	)	$	3,766	$	3,759	$	89	$	—		$	3,848
Total	$	3,740	$	31	$	(5	)	$	3,766	$	3,759	$	89	$	—		$	3,848

Security fair values are established by an independent pricing service as of the dates indicated. The difference between amortized cost and fair value reflects current interest rates and represents the potential gain (loss) had the portfolio been liquidated on those dates. Security gains (losses) are realized only in the event of dispositions prior to maturity or other-than-temporary impairment. Securities with unrealized losses as of September 30, 2018 and December 31, 2017, and the length of time they were in continuous loss positions as of such dates are as follows (dollars in thousands):

	Less than 12 months					12 months or more					Total
September 30, 2018	Estimated fair value		Gross unrealized losses			Estimated fair value		Gross unrealized losses			Estimated fair value		Gross unrealized losses
U. S. government agency securities	$	1,827	$	(76	)	$	8,638	$	(513	)	$	10,465	$	(589	)
State and municipal securities		28,333		(1,134	)		7,531		(592	)		35,864		(1,726	)
Mortgage-backed securities		32,051		(871	)		73,151		(3,910	)		105,202		(4,781	)
Asset-backed securities		—		—			—		—			—		—
Other debt securities		5,518		(50	)		—		—			5,518		(50	)
Total temporarily impaired securities	$	67,729	$	(2,131	)	$	89,320	$	(5,015	)	$	157,049	$	(7,146	)

December 31, 2017
U. S. government agency securities	$	7,375	$	(90	)	$	1,912	$	(78	)	$	9,287	$	(168	)
State and municipal securities		7,490		(106	)		5,798		(116	)		13,288		(222	)
Mortgage-backed securities		29,832		(322	)		67,813		(1,392	)		97,645		(1,714	)
Asset-backed securities		—		—			16,377		(198	)		16,377		(198	)
Other debt securities		—		—			—		—			—		—
Total temporarily impaired securities	$	44,697	$	(518	)	$	91,900	$	(1,784	)	$	136,597	$	(2,302	)

As noted in the table above, as of September 30, 2018, the Company had unrealized losses of $7.1 million in its investment securities portfolio. The unrealized losses associated with these investment securities are driven by changes in interest rates and are recorded as a component of equity. These investment securities will continue to be monitored as a part of our ongoing impairment analysis. Management evaluates the financial performance of the issuers on a quarterly basis to determine if it is probable that the issuers can make all contractual principal and interest payments. If a shortfall in future cash flows is identified, a credit loss will be deemed to have occurred and will be recognized as a charge to earnings and a new cost basis for the security will be established.

Because the Company currently does not intend to sell any investment securities that have an unrealized loss at September 30, 2018, and it is not more-likely-than-not that we will be required to sell these investment securities before recovery of their amortized cost bases, which may be at maturity, we do not consider these securities to be other-than-temporarily impaired at September 30, 2018.

Securities with a market value of $148.7 million at September 30, 2018 were pledged to collateralize public deposits, derivative positions and Federal Home Loan Bank advances.

Results from sales of debt and equity securities were as follows (dollars in thousands):

	Nine Months Ended			Nine Months Ended
	September 30, 2018			September 30, 2017
Proceeds	$	5,778		$	34,299
Gross gains		107			99
Gross losses		(105	)		(57	)

The amortized cost and fair value of securities at September 30, 2018, by contractual maturity, are shown below (dollars in thousands). Expected maturities will differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. Securities not due at a single maturity date are shown separately.

	Available-for-sale				Held-to-maturity
	Amortized cost		Estimated fair value		Amortized cost		Estimated fair value
Due in less than one year	$	1,763	$	1,756	$	394	$	396
Due one to five years		21,080		21,095		3,346		3,370
Due five to ten years		28,383		27,302		—		—
Due beyond ten years		17,434		16,401		—		—
Mortgage-backed securities		109,983		105,202		—		—
Asset-backed securities		15,687		15,713		—		—
Total	$	194,330	$	187,469	$	3,740	$	3,766

Loans and Allowance for Loan Losses

9 Months Ended

Sep. 30, 2018

Receivables [Abstract]

Loans and Allowance for Loan Losses

NOTE 3 – LOANS AND ALLOWANCE FOR LOAN LOSSES

A summary of the loan portfolio as of September 30, 2018 and December 31, 2017 follows (dollars in thousands):

	September 30, 2018			December 31, 2017
Commercial real estate	$	404,753		$	350,622
Consumer real estate		112,957			102,581
Construction and land development		129,799			82,586
Commercial and industrial		398,626			373,248
Consumer		8,274			6,862
Other		19,793			31,983
Total		1,074,202			947,882
Less net unearned income		(332	)		(345	)
Total loans		1,073,870			947,537
Allowance for loan losses		(15,218	)		(13,721	)
Total loans, net	$	1,058,652		$	933,816

The adequacy of the allowance for loan losses (ALL) is assessed at the end of each quarter. The ALL includes a specific component related to loans that are individually evaluated for impairment and a general component related to loans that are segregated into homogenous pools and collectively evaluated for impairment. The ALL factors applied to these pools are an estimate of probable incurred losses based on management’s evaluation of historical net losses from loans with similar characteristics, which are adjusted by management to reflect current events, trends, and conditions. The adjustments include consideration of the following: changes in lending policies and procedures, economic conditions, nature and volume of the portfolio, experience of lending management, volume and severity of past due loans, quality of the loan review system, value of underlying collateral for collateral dependent loans, concentrations, and other external factors.

The Company categorizes loans into risk categories based on relevant information about the ability of borrowers to service their debt such as: current financial information, historical payment experience, credit documentation, public information, and current economic trends, among other factors. The Company analyzes all commercial loans, and consumer relationships with an outstanding balance greater than $500,000, individually and assigns each loan a risk rating. This analysis is performed on a continual basis by the relationship managers and credit department personnel. On at least an annual basis an independent party performs a formal credit risk review of a sample of the loan portfolio. Among other things, this review assesses the appropriateness of the loan’s risk rating. The Company uses the following definitions for risk ratings:

Special Mention – A special mention asset possesses deficiencies or potential weaknesses deserving of management’s attention. If uncorrected, such weaknesses or deficiencies may expose the Company to an increased risk of loss in the future.

Substandard – A substandard asset is inadequately protected by the current sound net worth and paying capacity of the obligor or of the collateral pledged, if any. Assets so classified must have a well-defined weakness or weaknesses that jeopardize the liquidation of the debt. They are characterized by the distinct possibility that the Company will sustain some loss if deficiencies are not corrected. Loss potential, while existing in the aggregate amount of substandard assets, does not have to exist in individual assets classified substandard.

Doubtful – A doubtful asset has all weaknesses inherent in one classified substandard, with the added characteristic that weaknesses make collection or liquidation in full, on the basis of existing facts, conditions, and values, highly questionable and improbable. The probability of loss is extremely high, but certain important and reasonable specific pending factors which may work to the advantage and strengthening of the asset exist, therefore, its classification as an estimated loss is deferred until a more exact status may be determined. Pending factors include proposed merger, acquisition or liquidation procedures, capital injection, perfecting liens on additional collateral, and refinancing plans.

Loans not falling into the criteria above are considered to be pass-rated loans. The Company utilizes six loan grades within the pass risk rating.

The following tables present the loan balances by category as well as risk rating (dollars in thousands):

	Non-impaired Loans
September 30, 2018	Pass/Watch		Special Mention		Substandard		Total Non-impaired		Total Impaired Loans		Total
Commercial real estate	$	402,254	$	—	$	1,353	$	403,607	$	1,146	$	404,753
Consumer real estate		112,640		—		225		112,865		92		112,957
Construction and land development		129,799		—		—		129,799		—		129,799
Commercial and industrial		379,446		6,992		6,769		393,207		5,419		398,626
Consumer		8,174		—		—		8,174		100		8,274
Other		19,793		—		—		19,793		—		19,793
Total	$	1,052,106	$	6,992	$	8,347	$	1,067,445	$	6,757	$	1,074,202

December 31, 2017
Commercial real estate	$	349,415	$	—	$	—	$	349,415	$	1,207	$	350,622
Consumer real estate		102,571		—		10		102,581		—		102,581
Construction and land development		82,586		—		—		82,586		—		82,586
Commercial and industrial		349,494		11,193		11,073		371,760		1,488		373,248
Consumer		6,849		—		13		6,862		—		6,862
Other		31,983		—		—		31,983		—		31,983
Total	$	922,898	$	11,193	$	11,096	$	945,187	$	2,695	$	947,882

None of the Company’s loans had a risk rating of “Doubtful” as of September 30, 2018 or December 31, 2017.

The following tables detail the changes in the ALL for the three and nine months ended September 30, 2018 and 2017 (dollars in thousands):

	Commercial real estate			Consumer real estate			Construction and land development		Commercial and industrial			Consumer			Other			Total
Three Months Ended September 30, 2018
Balance, beginning of period	$	3,551		$	1,057		$	1,764	$	7,779		$	120		$	434		$	14,705
Charged-off loans		—			—			—		—			—			—			—
Recoveries		6			1			—		22			3			—			32
Provision for loan losses		(412	)		(75	)		449		767			(30	)		(218	)		481
Balance, end of period	$	3,145		$	983		$	2,213	$	8,568		$	93		$	216		$	15,218

Three Months Ended September 30, 2017
Balance, beginning of period	$	3,533		$	1,081		$	911	$	6,395		$	57		$	477		$	12,454
Charged-off loans		—			—			—		—			—			—			—
Recoveries		3			—			—		1,860			—			—			1,863
Provision for loan losses		(242	)		(97	)		576		(306	)		22			(148	)		(195	)
Balance, end of period	$	3,294		$	984		$	1,487	$	7,949		$	79		$	329		$	14,122

	Commercial real estate			Consumer real estate			Construction and land development			Commercial and industrial			Consumer			Other			Total
Nine Months Ended September 30, 2018
Balance, beginning of period	$	3,324		$	1,063		$	1,628		$	7,209		$	91		$	406		$	13,721
Charged-off loans		—			—			—			(226	)		(25	)		—			(251	)
Recoveries		16			4			—			348			52			—			420
Provision for loan losses		(195	)		(84	)		585			1,237			(25	)		(190	)		1,328
Balance, end of period	$	3,145		$	983		$	2,213		$	8,568		$	93		$	216		$	15,218

Nine Months Ended September 30, 2017
Balance, beginning of period	$	2,655		$	1,013		$	1,574		$	5,618		$	76		$	698		$	11,634
Charged-off loans		—			—			—			(12,369	)		—			—			(12,369	)
Recoveries		4			—			—			1,862			91			—			1,957
Provision for loan losses		635			(29	)		(87	)		12,838			(88	)		(369	)		12,900
Balance, end of period	$	3,294		$	984		$	1,487		$	7,949		$	79		$	329		$	14,122

A breakdown of the ALL and the loan portfolio by loan category at September 30, 2018 and December 31, 2017 follows (dollars in thousands):

	Commercial real estate		Consumer real estate		Construction and land development		Commercial and industrial		Consumer		Other		Total
September 30, 2018
Allowance for Loan Losses:
Collectively evaluated for impairment	$	3,145	$	983	$	2,213	$	5,868	$	93	$	216	$	12,518
Individually evaluated for impairment		—		—		—		2,700		—		—		2,700
Balances, end of period	$	3,145	$	983	$	2,213	$	8,568	$	93	$	216	$	15,218
Loans:
Collectively evaluated for impairment	$	403,607	$	112,865	$	129,799	$	393,207	$	8,174	$	19,793	$	1,067,445
Individually evaluated for impairment		1,146		92		—		5,419		100		—		6,757
Balances, end of period	$	404,753	$	112,957	$	129,799	$	398,626	$	8,274	$	19,793	$	1,074,202

December 31, 2017
Allowance for Loan Losses:
Collectively evaluated for impairment	$	3,324	$	1,063	$	1,628	$	7,109	$	91	$	406	$	13,621
Individually evaluated for impairment		—		—		—		100		—		—		100
Balances, end of period	$	3,324	$	1,063	$	1,628	$	7,209	$	91	$	406	$	13,721
Loans:
Collectively evaluated for impairment	$	349,415	$	102,581	$	82,586	$	371,760	$	6,862	$	31,983	$	945,187
Individually evaluated for impairment		1,207		—		—		1,488		—		—		2,695
Balances, end of period	$	350,622	$	102,581	$	82,586	$	373,248	$	6,862	$	31,983	$	947,882

The following table presents the allocation of the ALL for each respective loan category with the corresponding percentage of the ALL in each category to total loans, net of deferred fees as of September 30, 2018 and December 31, 2017 (dollars in thousands):

	September 30, 2018					December 31, 2017
	Amount		Percent of total loans, net of deferred fees			Amount		Percent of total loans, net of deferred fees
Commercial real estate	$	3,145		0.29	%	$	3,324		0.35	%
Consumer real estate		983		0.09			1,063		0.11
Construction and land development		2,213		0.21			1,628		0.17
Commercial and industrial		8,568		0.80			7,209		0.77
Consumer		93		0.01			91		0.01
Other		216		0.02			406		0.04
Total allowance for loan losses	$	15,218		1.42	%	$	13,721		1.45	%

The following table presents the Company’s impaired loans that were evaluated for specific loss allowance as of September 30, 2018 and December 31, 2017 (dollars in thousands):


	September 30, 2018						December 31, 2017
	Recorded investment		Unpaid principal balance		Related allowance		Recorded investment		Unpaid principal balance		Related allowance
With no related allowance recorded:
Commercial real estate	$	1,146	$	1,617	$	—	$	1,207	$	1,645	$	—
Consumer real estate		92		92		—		—		—		—
Construction and land development		—		—		—		—		—		—
Commercial and industrial		—		—		—		—		—		—
Consumer		100		100		—		—		—		—
Other		—		—		—		—		—		—
Subtotal		1,338		1,809		—		1,207		1,645		—
With an allowance recorded:
Commercial real estate		—		—		—		—		—		—
Consumer real estate		—		—		—		—		—		—
Construction and land development		—		—		—		—		—		—
Commercial and industrial		5,419		5,419		2,700		1,488		2,770		100
Consumer		—		—		—		—		—		—
Other		—		—		—		—		—		—
Subtotal		5,419		5,419		2,700		1,488		2,770		100
Total	$	6,757	$	7,228	$	2,700	$	2,695	$	4,415	$	100

The following table presents information related to the average recorded investment and interest income recognized on impaired loans for the three and nine months ended September 30, 2018 and 2017 (dollars in thousands):

	Three Months Ended				Three Months Ended				Nine Months Ended				Nine Months Ended
	September 30, 2018				September 30, 2017				September 30, 2018				September 30, 2017
	Average recorded investment		Interest income recognized		Average recorded investment		Interest income recognized		Average recorded investment		Interest income recognized		Average recorded investment		Interest income recognized
With no related allowance recorded:
Commercial real estate	$	1,159	$	15	$	1,245	$	—	$	1,189	$	25	$	1,272	$	—
Consumer real estate		92		—		—		—		92		3		—		—
Construction and land development		—		—		—		—		—		—		—		—
Commercial and industrial		—		—		—		—		—		—		—		—
Consumer		100		—		—		—		100		3		—		—
Other		—		—		—		—		—		—		—		—
Subtotal		1,351		15		1,245		—		1,381		31		1,272		—
With an allowance recorded:
Commercial real estate		—		—		—		—		—		—		—		—
Consumer real estate		—		—		—		—		—		—		—		—
Construction and land development		—		—		—		—		—		—		—		—
Commercial and industrial		5,419		—		1,941		—		5,369		118		2,141		—
Consumer		—		—		—		—		—		—		—		—
Other		—		—		—		—		—		—		—		—
Subtotal		5,419		—		1,941		—		5,369		118		2,141		—
Total	$	6,770	$	15	$	3,186	$	—	$	6,750	$	149	$	3,413	$	—

Interest income recognized on a cash basis for impaired loans amounted to $15,000 and $25,000 for the three and nine months ended September 30, 2018. No interest income was recognized on a cash basis for impaired loans during the three or nine months ended September 30, 2017.

The following table presents the aging of the recorded investment in past-due loans as of September 30, 2018 and December 31, 2017 by class of loans (dollars in thousands):

	30 - 59		60 - 89		Greater Than
	Days		Days		89 Days		Total		Loans Not
	Past Due		Past Due		Past Due		Past Due		Past Due		Total
September 30, 2018
Commercial real estate	$	2,474	$	—	$	—	$	2,474	$	402,279	$	404,753
Consumer real estate		220		—		215		435		112,522		112,957
Construction and land development		133		—		—		133		129,666		129,799
Commercial and industrial		—		563		4,856		5,419		393,207		398,626
Consumer		—		—		—		—		8,274		8,274
Other		307		—		—		307		19,486		19,793
Total	$	3,134	$	563	$	5,071	$	8,768	$	1,065,434	$	1,074,202

December 31, 2017
Commercial real estate	$	—	$	—	$	—	$	—	$	350,622	$	350,622
Consumer real estate		—		—		218		218		102,363		102,581
Construction and land development		—		—		—		—		82,586		82,586
Commercial and industrial		1,967		209		—		2,176		371,072		373,248
Consumer		—		—		13		13		6,849		6,862
Other		—		—		—		—		31,983		31,983
Total	$	1,967	$	209	$	231	$	2,407	$	945,475	$	947,882

The following table presents the recorded investment in non-accrual loans, past due loans over 89 days outstanding and accruing and troubled debt restructurings (“TDR”) by class of loans as of September 30, 2018 and December 31, 2017 (dollars in thousands):

	Non-Accrual		Past Due Over 89 Days and Accruing		Troubled Debt Restructurings
September 30, 2018
Commercial real estate	$	—	$	—	$	1,146
Consumer real estate		92		215		—
Construction and land development		—		—		—
Commercial and industrial		5,419		—		—
Consumer		100		—		—
Other		—		—		—
Total	$	5,611	$	215	$	1,146

December 31, 2017
Commercial real estate	$	1,207	$	—	$	1,207
Consumer real estate		—		218		—
Construction and land development		—		—		—
Commercial and industrial		1,488		—		—
Consumer		—		13		—
Other		—		—		—
Total	$	2,695	$	231	$	1,207

As of September 30, 2018 and December 31, 2017, all loans classified as nonperforming were deemed to be impaired.

As of both September 30, 2018 and December 31, 2017, the Company had a recorded investment in TDR of $1.1 million. The Company had no specific allowance for those loans at September 30, 2018 or December 31, 2017 and there were no commitments to lend additional amounts. Loans accounted for as TDR include modifications from original terms such as those due to bankruptcy proceedings, certain modifications of amortization periods or extended suspension of principal payments due to customer financial difficulties. In order to determine whether a borrower is experiencing financial difficulty, an evaluation is performed of the probability that the borrower will be in payment default on any of its debt in the foreseeable future without the modification. This evaluation is performed under the Bank’s loan policy. Loans accounted for as TDR are individually evaluated for impairment.

There were no TDR identified during the three or nine months ended September 30, 2018 or 2017. There were no TDR for which there was a payment default within twelve months following the modification during the three or nine months ended September 30, 2018 or 2017.

A loan is considered to be in payment default once it is 30 days contractually past due under the modified terms.

- Definition

The entire disclosure for claims held for amounts due a entity, excluding financing receivables. Examples include, but are not limited to, trade accounts receivables, notes receivables, loans receivables. Includes disclosure for allowance for credit losses.

+ References + Details

Federal Home Loan Bank Advances

9 Months Ended

Sep. 30, 2018

Federal Home Loan Banks [Abstract]

Federal Home Loan Bank Advances

NOTE 4 – FEDERAL HOME LOAN BANK ADVANCES

The Company had outstanding borrowings totaling of $125.0 million and $70.0 million at September 30, 2018 and December 31, 2017, respectively, via various advances. These advances are non-callable; interest payments are due monthly, with principal due at maturity.

The following is a summary of the contractual maturities and average effective rates of outstanding advances (dollars in thousands):

	September 30, 2018					December 31, 2017
Year	Amount		Interest Rates			Amount		Interest Rates
2018	$	115,000		2.18	%	$	70,000		1.66	%
2019		10,000		2.45			—		—
2020		—		—			—		—
2021		—		—			—		—
2022		—		—			—		—
Thereafter		—		—			—		—
Total	$	125,000		2.21	%	$	70,000		1.66	%

Advances from the FHLB are collateralized by investment securities with a market value of $3.9 million, FHLB stock and certain commercial and residential real estate mortgage loans totaling $420.6 million under a blanket mortgage collateral agreement. At September 30, 2018, the amount of available credit from the FHLB totaled $59.4 million.

Accumulated Other Comprehensive Income (Loss)

9 Months Ended

Sep. 30, 2018

Accumulated Other Comprehensive Income Loss Net Of Tax [Abstract]

Accumulated Other Comprehensive Income (Loss)

NOTE 5 – ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS)

The following were changes in accumulated other comprehensive income (loss) by component, net of tax, for the nine months ended September 30, 2018 and 2017 (dollars in thousands):

				Unrealized Gains			Unrealized
	Gains and			and Losses			Losses on
	Losses on			on Available			Securities
	Cash Flow			for Sale			Transferred to
	Hedges			Securities			Held to Maturity			Total
Nine Months Ended September 30, 2018
Beginning Balance	$	(3,679	)	$	1,162		$	(10	)	$	(2,527	)
Other comprehensive income (loss) before reclassification, net of tax		1,800			(4,521	)		—			(2,721	)
Amounts reclassified from accumulated other comprehensive income (loss), net of tax		(642	)		(1	)		10			(633	)
Net current period other comprehensive income (loss)		1,158			(4,522	)		10			(3,354	)
Ending Balance	$	(2,521	)	$	(3,360	)	$	—		$	(5,881	)

Nine Months Ended September 30, 2017
Beginning Balance	$	(4,241	)	$	(698	)	$	(1,212	)	$	(6,151	)
Other comprehensive income (loss) before reclassification, net of tax		985			1,502			—			2,487
Amounts reclassified from accumulated other comprehensive income (loss), net of tax		(589	)		(26	)		100			(515	)
Net current period other comprehensive income (loss)		396			1,476			100			1,972
Ending Balance	$	(3,845	)	$	778		$	(1,112	)	$	(4,179	)

The following were significant amounts reclassified out of each component of accumulated other comprehensive income (loss) for the three and nine months ended September 30, 2018 and 2017 (dollars in thousands):

													Affected Line Item
Details about Accumulated Other	Three Months Ended September 30,						Nine Months Ended September 30,						in the Statement Where
Comprehensive Income Components	2018			2017			2018			2017			Net Income is Presented
Unrealized losses on cash flow hedges	$	(111	)	$	(109	)	$	(330	)	$	(322	)	Interest expense - money market
		(108	)		(168	)		(368	)		(267	)	Interest expense - Federal Home Loan Bank advances
		16			—			56			—		Income tax benefit
	$	(203	)	$	(277	)	$	(642	)	$	(589	)	Net of tax
Unrealized (gains) losses on available- for-sale securities	$	1		$	(9	)	$	(2	)	$	(42	)	Net (gain) loss on sale of securities
		—			3			1			16		Income tax expense
	$	1		$	(6	)	$	(1	)	$	(26	)	Net of tax
Unrealized losses on securities transferred to held-to-maturity	$	—		$	79		$	14		$	162		Interest income - securities
		—			(30	)		(4	)		(62	)	Income tax benefit
	$	—		$	49		$	10		$	100		Net of tax

Income Taxes	9 Months Ended
Income Taxes	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Income Taxes	NOTE 6 – INCOME TAXES The Company’s effective tax rate for the three and nine months ended September 30, 2018 was 13.2% and 14.1% compared to 25.5% and 9.1% for the three and nine months ended September 30, 2017. In March 2016, the FASB issued guidance to simplify several aspects of the accounting for share-based payment award transactions, including income tax consequences. In addition to other changes, the guidance changes the accounting for excess tax benefits and tax deficiencies from generally being recognized in additional paid-in capital to recognition as income tax expense or benefit in the period they occur. The Company adopted the new guidance in the first quarter of 2017. As a result, the Company’s income tax expense was reduced by $422,000 and $1,062,000 for the three and nine months ended September 30, 2018, respectively, and by $144,000 and $310,000 for the three and nine months ended September 30, 2017, respectively. On December 22, 2017, Public Law 115-97, informally referred to as the Tax Cuts and Jobs Act (the “Tax Reform Act”) was enacted into law. The Tax Reform Act provides for significant changes to the U.S. tax code that impact businesses. Effective January 1, 2018, the Tax Reform Act reduced the U.S. federal tax rate for corporations from 35% to 21% for U.S. taxable income. The effective tax rate compared favorably to the statutory federal rate of 21% and Tennessee excise tax rate of 6.5% primarily due to investments in qualified municipal securities, company owned life insurance, state tax credits, net of the effect of certain non-deductible expenses and the recognition of excess tax benefits related to stock compensation.

Commitments and Contingencies

9 Months Ended

Sep. 30, 2018

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

NOTE 7 – COMMITMENTS AND CONTINGENCIES

In the normal course of business, the Company has outstanding commitments and contingent liabilities, such as commitments to extend credit and standby letters of credit, which are not included in the accompanying financial statements. The Company’s exposure to credit loss in the event of nonperformance by the other party to the financial instruments for commitments to extend credit and standby letters of credit is represented by the contractual or notional amount of those instruments. The Company uses the same credit policies in making such commitments as it does for instruments that are included in the balance sheet.

The following table sets forth outstanding financial instruments whose contract amounts represent credit risk as of September 30, 2018 and December 31, 2017 (dollars in thousands):

	Contract or notional amount
	September 30, 2018		December 31, 2017
Financial instruments whose contract amounts represent credit risk:
Unused commitments to extend credit	$	622,212	$	584,494
Standby letters of credit		11,526		11,552
Total	$	633,738	$	596,046

The Company is party to litigation and claims arising in the normal course of business. Management believes that the liabilities, if any, arising from such litigation and claims as of September 30, 2018, will not have a material impact on the financial statements of the Company.

Derivatives

9 Months Ended

Sep. 30, 2018

Derivative Instruments And Hedging Activities Disclosure [Abstract]

Derivatives

NOTE 8 – DERIVATIVES

The Company utilizes interest rate swap agreements as part of its asset liability management strategy to help manage its interest rate risk position. The notional amount of the interest rate swaps does not represent amounts exchanged by the parties. The amount exchanged is determined by reference to the notional amount and the other terms of the individual interest rate swap agreements.

Interest Rate Swaps Designated as Cash Flow Hedges

Forward starting interest rate swaps with notional amounts totaling $20 million as of September 30, 2018 and December 31, 2017 were designated as cash flow hedges of certain liabilities and were determined to be fully effective during all periods presented. As such, no amount of ineffectiveness has been included in net income. Therefore, the aggregate fair value of the swaps is recorded in other assets (liabilities) with changes in fair value recorded in other comprehensive income (loss). The amount included in accumulated other comprehensive income (loss) would be reclassified to current earnings should the hedges no longer be considered effective. The Company expects the hedges to remain fully effective during the remaining terms of the swaps.

Summary information about the interest-rate swaps designated as cash flow hedges was as follows (dollars in thousands):

	September 30, 2018			December 31, 2017
Notional amounts	$	20,000		$	20,000
Weighted average pay rates		3.54	%		3.54	%
Weighted average receive rates	3 month LIBOR			3 month LIBOR
Weighted average maturity	4.7 years			5.5 years
Fair value	$	(462	)	$	(1,375	)
Amount of unrealized loss recognized in accumulated other comprehensive income, net of tax	$	(341	)	$	(1,016	)

Pursuant to its interest rate swap agreements, the Company pledged collateral to the counterparties in the form of investment securities with a market value of $2.1 million at September 30, 2018. There was no collateral posted from the counterparties to the Company as of September 30, 2018. It is possible that the Company may need to post additional collateral in the future or that the counterparties may be required to post collateral to the Company in the future.

Other Interest Rate Swaps

The Company also enters into swaps to facilitate customer transactions and meet their financing needs. Upon entering into these transactions the Company enters into offsetting positions with large U.S. financial institutions in order to minimize risk to the Company. A summary of the Company’s customer related interest rate swaps was as follows (dollars in thousands):

	September 30, 2018					December 31, 2017
	Notional		Estimated			Notional		Estimated
	amount		fair value			amount		fair value
Interest rate swap agreements:
Pay fixed/receive variable swaps	$	37,199	$	492		$	41,863	$	55
Pay variable/receive fixed swaps		37,199		(492	)		41,863		(55	)
Total	$	74,398	$	—		$	83,726	$	—

Stock Options and Restricted Shares

9 Months Ended

Sep. 30, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock Options and Restricted Shares

NOTE 9 - STOCK OPTIONS AND RESTRICTED SHARES

During 2008, the board of directors of the Bank approved the CapStar Bank 2008 Stock Incentive Plan. Following the formation of CapStar Financial Holdings, Inc. in 2016, and in connection with the Share Exchange, the outstanding awards of restricted stock and stock options under the CapStar Bank 2008 Stock Incentive Plan were exchanged for similar awards of restricted stock and stock options issued by CapStar Financial Holdings, Inc. under the CapStar Financial Holdings, Inc. Stock Incentive Plan (the “Plan”), which the board of directors adopted in 2016. The Stock Incentive Plan provides for the grant of stock-based incentives, including stock options, restricted stock units, performance awards and restricted stock, to employees, directors and service providers that are subject to forfeiture until vesting conditions have been satisfied by the award recipient under the terms of the award. The Plan is intended to help align the interests of employees and our shareholders and reward our employees for improved Company performance. The Plan reserved 1,569,475 shares of stock for issuance of stock incentives. In April 2018 the board of directors reserved an additional 400,000 shares of stock for issuance of stock incentives. Stock incentives include both restricted share and stock option grants. Total shares issuable under the plan were 506,435 at September 30, 2018.

The Company has recognized stock-based compensation expense, within salaries and employee benefits for employees, and within other non-interest expense for directors, in the consolidated statements of income as follows (dollars in thousands):

	Three Months Ended						Nine Months Ended
	September 30,						September 30,
	2018			2017			2018			2017
Stock-based compensation expense before income taxes	$	310		$	288		$	940		$	771
Less: deferred tax benefit		(81	)		(110	)		(246	)		(295	)
Reduction of net income	$	229		$	178		$	694		$	476

Restricted Shares

Compensation expense is recognized over the vesting period of the awards based on the fair value of the stock at the issue date. The fair value of each restricted stock grant is based on valuations performed by independent consultants. The recipients have the right to vote and receive dividends but cannot sell, transfer, assign, pledge, hypothecate, or otherwise encumber the restricted stock until the shares have vested. Restricted shares fully vest on the third anniversary of the grant date. A summary of the changes in the Company’s nonvested restricted shares for the nine months ended September 30, 2018 follows:

				Weighted
				Average
	Restricted			Grant Date
Nonvested Shares	Shares			Fair Value
Nonvested at beginning of period		187,253		$	14.21
Granted		53,869			19.11
Vested		(99,603	)		12.61
Forfeited		(8,065	)		15.95
Nonvested at end of period		133,454		$	17.28

As of September 30, 2018, there was $1.6 million of unrecognized compensation cost related to nonvested shares granted under the Plan. The cost is expected to be recognized over a weighted-average period of 2.0 years. The total fair value of shares vested during the nine months ended September 30, 2018 and 2017 was $1.9 million and $1.1 million.

Stock Options

Option awards are generally granted with an exercise price equal to the fair value of the Company’s common stock at the date of grant. Option awards generally have a four year vesting period and a ten year contractual term.

The fair value of each option grant is estimated on the date of grant using the Black Scholes option pricing model. There were no options granted in 2018 or 2017.

A summary of the activity in stock options for the nine months ended September 30, 2018 follows:

						Weighted
				Weighted		Average
				Average		Remaining
				Exercise		Contractual
	Shares			Price		Term (years)
Outstanding at beginning of period		804,800		$	10.59
Granted		—			—
Exercised		(508,834	)		10.11
Forfeited or expired		—			—
Outstanding at end of period		295,966		$	11.43		4.0
Fully vested and expected to vest		294,134		$	11.42		3.7
Exercisable at end of period		268,466		$	11.34		3.7

Information related to stock options during each year follows:

	2018		2017
Intrinsic value of options exercised	$	4,282,055	$	684,275
Cash received from option exercises		5,144,090		821,500
Tax benefit realized from option exercises		1,119,329		263,446
Weighted average fair value of options granted		—		—

As of September 30, 2018, there was $0.1 million of unrecognized compensation cost related to nonvested stock options granted under the Plan. The cost is expected to be recognized over a weighted-average period of 1.0 year.

Regulatory Capital Requirements

9 Months Ended

Sep. 30, 2018

Banking And Thrift [Abstract]

Regulatory Capital Requirements

NOTE 10 – REGULATORY CAPITAL REQUIREMENTS

The Company and the Bank are subject to regulatory capital requirements administered by the Federal Reserve and the Bank is also subject to the regulatory capital requirements of the Tennessee Department of Financial Institutions. Failure to meet capital requirements can initiate certain mandatory – and possibly additional discretionary – actions by regulators that could, in that event, have a material adverse effect on the institutions’ financial statements. The relevant regulations require the Company and the Bank to meet specific capital adequacy guidelines that involve quantitative measures of their assets, liabilities and certain off-balance-sheet items as calculated under regulatory accounting principles. The capital classifications of the Company and the Bank are also subject to qualitative judgments by their regulators about components, risk weightings, and other factors. Those qualitative judgments could also affect the capital status of the Company and the Bank and the amount of dividends the Company and the Bank may distribute. The final rules implementing the Basel Committee on Banking Supervision’s capital guidelines for U.S. banks (Basel III rules) became effective for the Bank on January 1, 2015 with full compliance with all of the requirements being phased in over a multi-year schedule, and fully phased in by January 1, 2019. The net unrealized gain or loss on available for sale securities is not included in computing regulatory capital. Management believes as of September 30, 2018, the Company and the Bank met all regulatory capital adequacy requirements to which they are subject.

The Company’s and the Bank’s capital amounts and ratios as of September 30, 2018 and December 31, 2017 are presented in the following table (dollars in thousands).

	Actual					Minimum capital requirement (1)					Minimum to be well-capitalized (2)
	Amount		Ratio			Amount		Ratio			Amount		Ratio
At September 30, 2018:
Total capital to risk-weighted assets:
CapStar Financial Holdings, Inc.	$	171,866		12.62	%	$	108,958		8.00	%	N/A		N/A
CapStar Bank		154,906		11.38			108,897		8.00		$	136,122		10.00
Tier I capital to risk-weighted assets:
CapStar Financial Holdings, Inc.		156,469		11.49			81,718		6.00		N/A		N/A
CapStar Bank		139,509		10.25			81,673		6.00			108,897		8.00
Common equity Tier 1 capital to risk weighted assets:
CapStar Financial Holdings, Inc.		147,469		10.83			61,289		4.50		N/A		N/A
CapStar Bank		123,009		9.04			61,255		4.50			88,479		6.50
Tier I capital to average assets:
CapStar Financial Holdings, Inc.		156,469		11.02			56,770		4.00		N/A		N/A
CapStar Bank		139,509		9.83			56,760		4.00			70,950		5.00

At December 31, 2017:
Total capital to risk-weighted assets:
CapStar Financial Holdings, Inc.	$	156,434		12.52	%	$	99,932		8.00	%	N/A		N/A
CapStar Bank		142,396		11.40			99,928		8.00		$	124,909		10.00
Tier I capital to risk-weighted assets:
CapStar Financial Holdings, Inc.		142,534		11.41			74,949		6.00		N/A		N/A
CapStar Bank		128,496		10.29			74,946		6.00			99,928		8.00
Common equity Tier 1 capital to risk weighted assets:
CapStar Financial Holdings, Inc.		133,703		10.70			56,212		4.50		N/A		N/A
CapStar Bank		112,165		8.98			56,209		4.50			81,191		6.50
Tier I capital to average assets:
CapStar Financial Holdings, Inc.		142,534		10.77			53,218		4.00		N/A		N/A
CapStar Bank		128,496		9.71			53,215		4.00			66,519		5.00

(1)

For the calendar year 2018, the Company must maintain a capital conservation buffer of Tier 1 common equity capital in excess of minimum risk-based capital ratios by at least 1.875% to avoid limits on capital distributions and certain discretionary bonus payments to executive officers and similar employees.

(2)

For the Company to be well-capitalized, the Bank must be well-capitalized and the Company must not be subject to any written agreement, order, capital directive, or prompt corrective action directive issued by the Federal Reserve to meet and maintain a specific capital level for any capital measure.

- Definition

The entire disclosure for banks, savings institutions, and credit unions, for regulatory capital requirements imposed by the Federal Reserve System (FRB), the Federal Deposit Insurance Corporation (FDIC), the Office of Thrift Supervision (OTS) or for any state imposed capital requirements, as applicable. The disclosure may include (1) a description of regulatory capital requirements (a) for capital adequacy purposes and (b) established by the prompt corrective action provisions of Section 38 of the Federal Depository Insurance Act; (2) the actual or possible material effects of noncompliance with such requirements; (3) whether the entity is in compliance with the regulatory capital requirements including (a) required and actual ratios and amounts of Tier 1 leverage, Tier 1 risk-based, and total risk-based capital, tangible capital (for savings institutions), and Tier 3 capital for market risk (for certain banks and bank holding companies), (b) factors that may significantly affect capital adequacy; (4) the prompt corrective action category in which the entity was classified as of its most recent notification; (5) whether management believes any conditions or events since notification have changed the entity's category. Also may include additional information that might be disclosed in situations where substantial doubt about the entity's ability to continue as a going concern for a reasonable period of time.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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Reference 8: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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Reference 9: http://fasb.org/us-gaap/role/ref/legacyRef
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+ Details

Earnings Per Share

9 Months Ended

Sep. 30, 2018

Earnings Per Share [Abstract]

Earnings Per Share

NOTE 11 – EARNINGS PER SHARE

The following is a summary of the basic and diluted earnings per share calculation for the three and nine months ended September 30, 2018 and 2017 (dollars in thousands, except share data):

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2018		2017		2018		2017
Basic net income per share calculation:
Numerator – Net income	$	3,656	$	4,419	$	10,363	$	1,409
Denominator – Average common shares outstanding		12,040,229		11,279,364		11,851,476		11,239,093
Basic net income per share	$	0.30	$	0.39	$	0.87	$	0.13
Diluted net income per share calculation:
Numerator – Net income	$	3,656	$	4,419	$	10,363	$	1,409
Denominator – Average common shares outstanding		12,040,229		11,279,364		11,851,476		11,239,093
Dilutive shares contingently issuable		1,073,546		1,471,059		1,201,282		1,518,998
Average diluted common shares outstanding		13,113,775		12,750,423		13,052,758		12,758,091
Diluted net income per share	$	0.28	$	0.35	$	0.79	$	0.11

Fair Value

9 Months Ended

Sep. 30, 2018

Fair Value Disclosures [Abstract]

Fair Value

NOTE 12 – FAIR VALUE

Fair value is the exchange price that would be received for an asset or paid to transfer a liability (exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. There are three levels of inputs that may be used to measure fair values:

Level 1:

Quoted prices (unadjusted) for identical assets or liabilities in active markets that the entity has the ability to access as of the measurement date.

Level 2:

Significant observable inputs other than Level 1 prices such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data.

Level 3:

Significant unobservable inputs that reflect a reporting entity’s own assumptions about the assumptions that market participants would use in pricing an asset or liability.

The Bank used the following methods and significant assumptions to estimate fair value:

Investment Securities: The fair values for investment securities are determined by quoted market prices, if available (Level 1). For securities where quoted prices are not available, fair values are calculated based on market prices of similar securities (Level 2), using matrix pricing. Matrix pricing is a mathematical technique commonly used to price debt securities that are not actively traded and, values debt securities by relying on quoted prices for the specific securities and the securities’ relationship to other benchmark quoted securities (Level 2 inputs). For securities where quoted prices or market prices of similar securities are not available, fair values are calculated using discounted cash flows or other market indicators (Level 3). See below for additional discussion of Level 3 valuation methodologies and significant inputs. The fair values of all securities are determined from third party pricing services without adjustment.

Derivatives-Interest Rate Swaps: The fair values of derivatives are based on valuation models using observable market data as of the measurement date (Level 2). The Bank’s derivatives are traded in an over-the-counter market where quoted market prices are not always available. Therefore, the fair values of derivatives are determined using quantitative models that utilize multiple market inputs. The inputs will vary based on the type of derivative, but could include interest rates, prices and indices to generate continuous yield or pricing curves, prepayment rates, and volatility factors to value the position. The majority of market inputs are actively quoted and can be validated through external sources, including brokers, market transactions and third-party pricing services. The fair values of all interest rate swaps are determined from third party pricing services without adjustment.

Impaired Loans: The fair value of impaired loans with specific allocations of the allowance for loan losses is generally based on recent appraisals. These appraisals may utilize a single valuation approach or a combination of approaches including comparable sales and the income approach. Adjustments are routinely made in the appraisal process by the independent appraisers to adjust for differences between the comparable sales and income data available for similar loans and collateral underlying such loans. Such adjustments result in a Level 3 classification of the inputs for determining fair value. Collateral may be valued using an appraisal, net book value per the borrower’s financial statements, or aging reports, adjusted or discounted based on management’s historical knowledge, changes in market conditions from the time of the valuation, and management’s expertise and knowledge of the client and client’s business, resulting in a Level 3 fair value classification. Impaired loans are evaluated on at least a quarterly basis for additional impairment and adjusted in accordance with the loan policy.

Other Real Estate Owned: Assets acquired through or instead of loan foreclosure are initially recorded at fair value less costs to sell when acquired, establishing a new cost basis. These assets are subsequently accounted for at lower of cost or fair value less estimated costs to sell. Fair value is commonly based on recent real estate appraisals which are updated no less frequently than annually. These appraisals may utilize a single valuation approach or a combination of approaches including comparable sales and the income approach with data from comparable properties. Adjustments are routinely made in the appraisal process by the independent appraisers to adjust for differences between the comparable sales and income data available. Appraisals may be adjusted or discounted based on management’s historical knowledge, changes in market conditions from the time of the valuation, and/or management’s expertise and knowledge of the collateral. Such adjustments result in a Level 3 classification of the inputs for determining fair value. Real estate owned properties are evaluated on a quarterly basis for additional impairment and adjusted accordingly. The Company had no other real estate owned at September 30, 2018 or December 31, 2017.

Loans Held For Sale: Loans held for sale are carried at the lower of cost or fair value, which is evaluated on a pool-level basis. The fair value of loans held for sale is determined using quoted prices for similar assets, adjusted for specific attributes of that loan or other observable market data, such as outstanding commitments from third party investors (Level 2). There were no loans held for sale carried at fair value at September 30, 2018 or December 31, 2017.

Assets and liabilities measured at fair value on a recurring basis are summarized below (dollars in thousands):

	Fair value measurements at September 30, 2018
				Quoted prices
				in active		Significant
				markets for		other			Significant
				identical		observable			unobservable
	Carrying			assets		inputs			inputs
	Value			(Level 1)		(Level 2)			(Level 3)
Assets:
Securities available-for-sale:
U.S. government-sponsored agencies	$	10,465		$	—	$	10,465		$	—
Obligations of states and political subdivisions		44,245			—		44,245			—
Mortgage-backed securities-residential		105,202			—		105,202			—
Asset-backed securities		15,713			—		15,713			—
Other debt securities		11,844			—		11,844			—
Total securities available-for-sale	$	187,469		$	—	$	187,469		$	—
Derivatives:
Interest rate swaps - customer related	$	624		$	—	$	624		$	—
Liabilities:
Derivatives:
Interest rate swaps - customer related	$	(624	)	$	—	$	(624	)	$	—
Interest rate swaps - cash flow hedges		(462	)		—		(462	)		—
Total derivatives	$	(1,086	)	$	—	$	(1,086	)	$	—

	Fair value measurements at December 31, 2017
				Quoted prices
				in active		Significant
				markets for		other			Significant
				identical		observable			unobservable
	Carrying			assets		inputs			inputs
	Value			(Level 1)		(Level 2)			(Level 3)
Assets:
Securities available-for-sale:
U.S. government-sponsored agencies	$	11,277		$	—	$	11,277		$	—
Obligations of states and political subdivisions		52,998			—		52,998			—
Mortgage-backed securities-residential		106,562			—		106,562			—
Asset-backed securities		16,377			—		16,377			—
Other debt securities		5,407			—		5,407			—
Total securities available-for-sale	$	192,621		$	—	$	192,621		$	—
Derivatives:
Interest rate swaps - customer related	$	184		$	—	$	184		$	—
Liabilities:
Derivatives:
Interest rate swaps - customer related	$	(184	)	$	—	$	(184	)	$	—
Interest rate swaps - cash flow hedges		(1,375	)		—		(1,375	)		—
Total derivatives	$	(1,559	)	$	—	$	(1,559	)	$	—

Assets measured at fair value on a nonrecurring basis are summarized below (dollars in thousands):

Fair value measurements at September 30, 2018

Quoted prices

in active

Significant

markets for

other

Significant

identical

observable

unobservable

Carrying

assets

inputs

Value

(level 1)

(level 2)

(level 3)

Assets:

Impaired loans:

Commercial and industrial

2,719

—

2,719

Fair value measurements at December 31, 2017

Quoted prices

in active

Significant

markets for

other

Significant

identical

observable

unobservable

Carrying

assets

inputs

Value

(level 1)

(level 2)

(level 3)

Assets:

Impaired loans:

Commercial and industrial

1,388

—

1,388

The following table presents quantitative information about Level 3 fair value measurements for assets measured at fair value on a non-recurring basis at September 30, 2018 and December 31, 2017 (dollars in thousands):

					Range
	Fair		Valuation		(Weighted-
September 30, 2018	Value		Technique(s)	Unobservable Input(s)	Average)
Impaired loans:
Commercial and industrial	$	2,719	Discounted cash flow	Probability of default	5%-60%
				Loss severity	5%-50%

Range

Fair

Valuation

(Weighted-

December 31, 2017

Value

Technique(s)

Unobservable Input(s)

Average)

Impaired loans:

Commercial and industrial

1,388

Sales comparison approach

Appraisal discounts

Fair Value of Financial Instruments

The carrying value and estimated fair values of the Bank’s financial instruments at September 30, 2018 and December 31, 2017 were as follows (dollars in thousands):

	September 30, 2018				December 31, 2017
	Carrying				Carrying				Fair value
	amount		Fair value		amount		Fair value		level of input
Financial assets:
Cash and due from banks, interest-bearing deposits in financial institutions	$	49,842	$	49,842	$	78,078	$	78,078	Level 1
Federal funds sold		2,747		2,747		4,719		4,719	Level 1
Securities available-for-sale		187,469		187,469		192,621		192,621	Level 2
Securities held-to-maturity		3,740		3,766		3,759		3,848	Level 2
Loans held for sale		50,499		51,326		74,093		75,549	Level 2
Restricted equity securities		8,817	N/A			8,806	N/A		N/A
Loans, net		1,073,870		1,065,226		947,537		944,037	Level 3
Accrued interest receivable		4,430		4,430		4,084		4,084	Level 2
Other assets		23,519		23,519		22,663		22,663	Level 2
Financial liabilities:
Deposits		1,126,403		1,074,725		1,119,866		1,065,669	Level 3
Federal Home Loan Bank advances		125,000		124,983		70,000		69,980	Level 2
Other liabilities		2,447		2,447		3,672		3,672	Level 3

The methods and assumptions, not previously presented, used to estimate fair values are described as follows:

(a)	Cash and Due from Banks, Interest-Bearing Deposits in Financial Institutions

For these short‑term instruments, the carrying amount is a reasonable estimate of fair value.

(b)	Federal Funds Sold

Federal funds sold clear on a daily basis. For this reason, the carrying amount is a reasonable estimate of fair value.

(c)	Restricted Equity Securities

It is not practical to determine the fair value of restricted securities due to restrictions placed on their transferability.

(d)	Loans, net

During the first quarter of 2018, the Company adopted ASU 2016-01, “Recognition and Measurement of Financial Assets and Liabilities.” The amendments included within this standard, which are applied prospectively, require the Company to disclose fair value of financial instruments measured at amortized cost on the balance sheet to measure that fair value using an exit price notion. Prior to adopting the amendments included in the standard, the Company was allowed to measure fair value under an entry price notion. The entry price notion previously applied by the Company used a discounted cash flows technique to calculate the present value of expected future cash flows for a financial instrument. The exit price notion uses the same approach, but also incorporates other factors, such as enhanced credit risk, illiquidity risk and market factors that sometimes exist in exit prices in dislocated markets.

As of September 30, 2018, the technique used by the Company to estimate the exit price of the loan portfolio consists of similar procedures to those used as of December 31, 2017, but with added emphasis on both illiquidity risk and credit risk not captured by the previously applied entry price notion. The fair value of the Company’s loan portfolio has always included a credit risk assumption in the determination of the fair value of its loans. This credit risk assumption is intended to approximate the fair value that a market participant would realize in a hypothetical orderly transaction. The Company’s loan portfolio is initially fair valued using a segmented approach. The Company divides its loan portfolio into the following categories: variable rate loans, impaired loans and all other loans. The results are then adjusted to account for credit risk as described above. However, under the new guidance, the Company believes a further credit risk discount must be applied through the use of a discounted cash flow model to compensate for illiquidity risk, based on certain assumptions included within the discounted cash flow model, primarily the use of discount rates that better capture inherent credit risk over the lifetime of a loan. This consideration of enhanced credit risk provides an estimated exit price for the Company’s loan portfolio.

For variable-rate loans that reprice frequently and have no significant change in credit risk, fair values approximate carrying values. Fair values for impaired loans are estimated using discounted cash flow models or based on the fair value of the underlying collateral.

As of December 31, 2017, the fair value of the Company’s loan portfolio includes a credit risk assumption in the determination of the fair value of its loans. This credit risk assumption is intended to approximate the fair value that a market participant would realize in a hypothetical orderly transaction. The Company’s loan portfolio is initially fair valued using a segmented approach. The Company divides its loan portfolio into the following categories: variable rate loans, impaired loans and all other loans. The results are then adjusted to account for credit risk. For variable-rate loans that reprice frequently and have no significant change in credit risk, fair values approximate carrying values. Fair values for impaired loans are estimated using discounted cash flow models or based on the fair value of the underlying collateral. For other loans, fair values are estimated using discounted cash flow models, using current market interest rates offered for loans with similar terms to borrowers of similar credit quality. The values derived from the discounted cash flow approach for each of the above portfolios are then further discounted to incorporate credit risk. The methods utilized to estimate the fair value of loans do not necessarily represent an exit price as of December 31, 2017.

(e)	Accrued Interest Receivable

The carrying amounts of accrued interest approximate fair value.

(f)	Other Assets

Included in other assets are bank owned life insurance, certain interest rate swap agreements and the cash flow hedge relationships. The fair values of interest rate swap agreements and the cash flow hedge relationships are based on independent pricing services that utilize pricing models with observable market inputs. For bank owned life insurance, the carrying amount is based on the cash surrender value and is a reasonable estimate of fair value.

(g)

Deposits

The fair value of demand deposits, savings accounts and certain money market deposits is the amount payable on demand at the reporting date. The fair value of certificates of deposit is estimated by discounted cash flow models, using current market interest rates offered on certificates with similar remaining maturities.

(h)	Federal Home Loan Bank Advances

The fair value of fixed rate Federal Home Loan Bank Advances is estimated using discounted cash flow models, using current market interest rates offered on certificates, advances and other borrowings with similar remaining maturities.

(i)	Other Liabilities

Included in other liabilities are accrued interest payable, certain interest rate swap agreements, the cash flow hedge relationships and contingent consideration. The fair values of interest rate swap agreements and the cash flow hedge relationships are based on independent pricing services that utilize pricing models with observable market inputs. The fair value of contingent consideration is estimated by a discounted cash flow model that utilizes various unobservable inputs. The carrying amounts of accrued interest approximate fair value.

(j)	Off-Balance Sheet Instruments

Fair values for off-balance sheet, credit-related financial instruments are based on fees currently charged to enter into similar agreements, taking into account the remaining terms of the agreements and the counterparties’ credit standing. The fair value of commitments is not material.

(k)	Limitations

Fair value estimates are made at a specific point in time, based on relevant market information and information about the financial instruments. These estimates do not reflect any premium or discount that could result from offering for sale at one time the Bank’s entire holdings of a particular instrument. Because no market exists for a significant portion of the Bank’s financial instruments, fair value estimates are based on judgments regarding future expected loss experience, current economic conditions, risk characteristics of various financial instruments, and other factors. These estimates are subjective in nature and involve uncertainties and matters of significant judgment and, therefore, cannot be determined with precision. Changes in assumptions could significantly affect the estimates.

Fair value estimates are based on estimating on and off‑balance sheet financial instruments without attempting to estimate the value of anticipated future business and the value of assets and liabilities that are not considered financial instruments. For example, fixed assets are not considered financial instruments and their value has not been incorporated into the fair value estimates. In addition, the tax ramifications related to the realization of the unrealized gains and losses can have a significant effect on fair value estimates and have not been considered in the estimates.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Subsequent Events	9 Months Ended
Subsequent Events	Sep. 30, 2018
Subsequent Events [Abstract]
Subsequent Events	NOTE 13 – SUBSEQUENT EVENT On October 1, 2018, pursuant to the Agreement and Plan of Merger, dated as of June 11, 2018 (the “Merger Agreement”), by and between CapStar Financial Holdings, Inc., a Tennessee corporation (“CapStar”), and Athens Bancshares Corporation, a Tennessee corporation (“Athens”), Athens was merged with and into CapStar, with CapStar continuing as the surviving entity (the “Merger”). Immediately following the Merger, Athens Federal Community Bank, National Association, a wholly owned subsidiary of Athens, merged with and into CapStar Bank, a wholly owned subsidiary of CapStar (the “Bank Merger”), with CapStar Bank continuing as the surviving entity in the Bank Merger. On the terms and subject to the conditions set forth in the Merger Agreement, at the effective time of the Merger (the “Effective Time”), each share of common stock, par value $0.01, of Athens (“Athens Common Stock”) issued and outstanding immediately prior to the completion of the merger (other than dissenting shares and shares of Athens common stock owned directly or indirectly by Athens, CapStar and their wholly owned subsidiaries (in each case, other than shares of Athens common stock held in a fiduciary capacity or in connection with debts previously contracted) was converted into the right to receive 2.864 shares (the “Exchange Ratio”) of voting common stock, par value $1.00 per share, of CapStar (“CapStar Common Stock”), with cash paid in lieu of fractional shares. This resulted in the issuance of 5,181,916 shares of CapStar common stock on October 1, 2018. At the Effective Time, each outstanding and unexercised Athens stock option granted under the Athens Bancshares Corporation 2010 Equity Incentive Plan (the “Athens Equity Plan”) that was held by an employee or service provider of Athens who had terminated service prior to the Effective Time was cancelled and converted into the right to receive the cash value of the merger consideration (determined in accordance with the terms of the Merger Agreement), less the applicable option exercise price and less applicable withholding taxes. Except as described in the prior sentence, each outstanding and unexercised Athens stock option granted under the Athens Equity Plan was converted into an option to purchase shares of CapStar Common Stock, with the number of shares and exercise price adjusted to reflect the Exchange Ratio in accordance with the terms of the Merger Agreement. The converted options resulted in the right to purchase 548,051 shares of CapStar Common Stock at a weighted average exercise price of $5.06. Total acquisition consideration resulting from the Merger amounted to approximately $92.9 million. The foregoing description of the Merger Agreement does not purport to be complete and is qualified in its entirety by reference to the full text of the Merger Agreement, a copy of which was attached as Exhibit 2.1 to CapStar’s Form 8-K filed with the U.S. Securities and Exchange Commission on June 14, 2018 and the terms of which are incorporated herein by reference.

Summary of Significant Accounting Policies (Policies)	9 Months Ended
Summary of Significant Accounting Policies (Policies)	Sep. 30, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited consolidated financial statements as of and for the period ended September 30, 2018 include CapStar Financial Holdings, Inc. and its wholly owned subsidiary, CapStar Bank (the “Bank”, together referred to as the “Company”). Significant intercompany transactions and accounts are eliminated in consolidation. The accompanying unaudited consolidated financial statements have been prepared in accordance with instructions to Form 10-Q and do not include all information and footnotes required by U.S. generally accepted accounting principles (“U.S. GAAP”) for complete financial statements. All adjustments consisting of normally recurring accruals that, in the opinion of management, are necessary for a fair presentation of the financial position and results of operations for the periods presented have been included. These unaudited consolidated financial statements should be read in conjunction with the Company’s consolidated financial statements and related notes appearing in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Material estimates that are particularly susceptible to significant change relate to the determination of the allowance for loan losses, determination of impairment of intangible assets, including goodwill, the valuation of our investment portfolio, deferred tax assets and estimated liabilities. There have been no significant changes to the Company’s critical accounting policies as disclosed in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017.
Subsequent Events	Subsequent Events Accounting Standards Codification (“ASC”) 855, Subsequent Events, establishes general standards of accounting for and disclosure of events that occur after the balance sheet date but before financial statements are issued. The Company evaluated all events or transactions that occurred after September 30, 2018 through the date of the issued financial statements.

Securities (Tables)

9 Months Ended

Sep. 30, 2018

Investments Debt And Equity Securities [Abstract]

Summary of Amortized Cost and Fair Value of Available-for-sale and Held-to-maturity Securities

The amortized cost and fair value of securities available-for-sale and held-to-maturity at September 30, 2018 and December 31, 2017 are summarized as follows (dollars in thousands):

	September 30, 2018									December 31, 2017
	Amortized Cost		Gross unrealized gains		Gross unrealized (losses)			Estimated fair value		Amortized Cost		Gross unrealized gains		Gross unrealized (losses)			Estimated fair value
Securities available-for-sale:
U. S. government agency securities	$	11,054	$	—	$	(589	)	$	10,465	$	11,433	$	12	$	(168	)	$	11,277
State and municipal securities		45,738		228		(1,721	)		44,245		51,790		1,430		(222	)		52,998
Mortgage-backed securities		109,983		—		(4,781	)		105,202		108,236		40		(1,714	)		106,562
Asset-backed securities		15,687		26		—			15,713		16,575		—		(198	)		16,377
Other debt securities		11,868		26		(50	)		11,844		5,326		81		—			5,407
Total	$	194,330	$	280	$	(7,141	)	$	187,469	$	193,360	$	1,563	$	(2,302	)	$	192,621
Securities held-to-maturity:
State and municipal securities	$	3,740	$	31	$	(5	)	$	3,766	$	3,759	$	89	$	—		$	3,848
Total	$	3,740	$	31	$	(5	)	$	3,766	$	3,759	$	89	$	—		$	3,848

Summary of Securities with Unrealized Losses and Length of Time Continuous Loss Positions

	Less than 12 months					12 months or more					Total
September 30, 2018	Estimated fair value		Gross unrealized losses			Estimated fair value		Gross unrealized losses			Estimated fair value		Gross unrealized losses
U. S. government agency securities	$	1,827	$	(76	)	$	8,638	$	(513	)	$	10,465	$	(589	)
State and municipal securities		28,333		(1,134	)		7,531		(592	)		35,864		(1,726	)
Mortgage-backed securities		32,051		(871	)		73,151		(3,910	)		105,202		(4,781	)
Asset-backed securities		—		—			—		—			—		—
Other debt securities		5,518		(50	)		—		—			5,518		(50	)
Total temporarily impaired securities	$	67,729	$	(2,131	)	$	89,320	$	(5,015	)	$	157,049	$	(7,146	)

December 31, 2017
U. S. government agency securities	$	7,375	$	(90	)	$	1,912	$	(78	)	$	9,287	$	(168	)
State and municipal securities		7,490		(106	)		5,798		(116	)		13,288		(222	)
Mortgage-backed securities		29,832		(322	)		67,813		(1,392	)		97,645		(1,714	)
Asset-backed securities		—		—			16,377		(198	)		16,377		(198	)
Other debt securities		—		—			—		—			—		—
Total temporarily impaired securities	$	44,697	$	(518	)	$	91,900	$	(1,784	)	$	136,597	$	(2,302	)

Summary of Sale of Debt and Equity Securities

Results from sales of debt and equity securities were as follows (dollars in thousands):

	Nine Months Ended			Nine Months Ended
	September 30, 2018			September 30, 2017
Proceeds	$	5,778		$	34,299
Gross gains		107			99
Gross losses		(105	)		(57	)

Summary of Amortized Cost and Fair Value of Debt Securities by Contractual Maturity

	Available-for-sale				Held-to-maturity
	Amortized cost		Estimated fair value		Amortized cost		Estimated fair value
Due in less than one year	$	1,763	$	1,756	$	394	$	396
Due one to five years		21,080		21,095		3,346		3,370
Due five to ten years		28,383		27,302		—		—
Due beyond ten years		17,434		16,401		—		—
Mortgage-backed securities		109,983		105,202		—		—
Asset-backed securities		15,687		15,713		—		—
Total	$	194,330	$	187,469	$	3,740	$	3,766

Loans and Allowance for Loan Losses (Tables)

9 Months Ended

Sep. 30, 2018

Receivables [Abstract]

Summary of Loan Portfolio

A summary of the loan portfolio as of September 30, 2018 and December 31, 2017 follows (dollars in thousands):

	September 30, 2018			December 31, 2017
Commercial real estate	$	404,753		$	350,622
Consumer real estate		112,957			102,581
Construction and land development		129,799			82,586
Commercial and industrial		398,626			373,248
Consumer		8,274			6,862
Other		19,793			31,983
Total		1,074,202			947,882
Less net unearned income		(332	)		(345	)
Total loans		1,073,870			947,537
Allowance for loan losses		(15,218	)		(13,721	)
Total loans, net	$	1,058,652		$	933,816

Summary of Loans by Risk Rating

The following tables present the loan balances by category as well as risk rating (dollars in thousands):

	Non-impaired Loans
September 30, 2018	Pass/Watch		Special Mention		Substandard		Total Non-impaired		Total Impaired Loans		Total
Commercial real estate	$	402,254	$	—	$	1,353	$	403,607	$	1,146	$	404,753
Consumer real estate		112,640		—		225		112,865		92		112,957
Construction and land development		129,799		—		—		129,799		—		129,799
Commercial and industrial		379,446		6,992		6,769		393,207		5,419		398,626
Consumer		8,174		—		—		8,174		100		8,274
Other		19,793		—		—		19,793		—		19,793
Total	$	1,052,106	$	6,992	$	8,347	$	1,067,445	$	6,757	$	1,074,202

December 31, 2017
Commercial real estate	$	349,415	$	—	$	—	$	349,415	$	1,207	$	350,622
Consumer real estate		102,571		—		10		102,581		—		102,581
Construction and land development		82,586		—		—		82,586		—		82,586
Commercial and industrial		349,494		11,193		11,073		371,760		1,488		373,248
Consumer		6,849		—		13		6,862		—		6,862
Other		31,983		—		—		31,983		—		31,983
Total	$	922,898	$	11,193	$	11,096	$	945,187	$	2,695	$	947,882

Summary of Changes and Breakdown of Allowance for Loan Losses and Loan Portfolio by Loan Category

The following tables detail the changes in the ALL for the three and nine months ended September 30, 2018 and 2017 (dollars in thousands):

	Commercial real estate			Consumer real estate			Construction and land development		Commercial and industrial			Consumer			Other			Total
Three Months Ended September 30, 2018
Balance, beginning of period	$	3,551		$	1,057		$	1,764	$	7,779		$	120		$	434		$	14,705
Charged-off loans		—			—			—		—			—			—			—
Recoveries		6			1			—		22			3			—			32
Provision for loan losses		(412	)		(75	)		449		767			(30	)		(218	)		481
Balance, end of period	$	3,145		$	983		$	2,213	$	8,568		$	93		$	216		$	15,218

Three Months Ended September 30, 2017
Balance, beginning of period	$	3,533		$	1,081		$	911	$	6,395		$	57		$	477		$	12,454
Charged-off loans		—			—			—		—			—			—			—
Recoveries		3			—			—		1,860			—			—			1,863
Provision for loan losses		(242	)		(97	)		576		(306	)		22			(148	)		(195	)
Balance, end of period	$	3,294		$	984		$	1,487	$	7,949		$	79		$	329		$	14,122

	Commercial real estate			Consumer real estate			Construction and land development			Commercial and industrial			Consumer			Other			Total
Nine Months Ended September 30, 2018
Balance, beginning of period	$	3,324		$	1,063		$	1,628		$	7,209		$	91		$	406		$	13,721
Charged-off loans		—			—			—			(226	)		(25	)		—			(251	)
Recoveries		16			4			—			348			52			—			420
Provision for loan losses		(195	)		(84	)		585			1,237			(25	)		(190	)		1,328
Balance, end of period	$	3,145		$	983		$	2,213		$	8,568		$	93		$	216		$	15,218

Nine Months Ended September 30, 2017
Balance, beginning of period	$	2,655		$	1,013		$	1,574		$	5,618		$	76		$	698		$	11,634
Charged-off loans		—			—			—			(12,369	)		—			—			(12,369	)
Recoveries		4			—			—			1,862			91			—			1,957
Provision for loan losses		635			(29	)		(87	)		12,838			(88	)		(369	)		12,900
Balance, end of period	$	3,294		$	984		$	1,487		$	7,949		$	79		$	329		$	14,122

A breakdown of the ALL and the loan portfolio by loan category at September 30, 2018 and December 31, 2017 follows (dollars in thousands):

	Commercial real estate		Consumer real estate		Construction and land development		Commercial and industrial		Consumer		Other		Total
September 30, 2018
Allowance for Loan Losses:
Collectively evaluated for impairment	$	3,145	$	983	$	2,213	$	5,868	$	93	$	216	$	12,518
Individually evaluated for impairment		—		—		—		2,700		—		—		2,700
Balances, end of period	$	3,145	$	983	$	2,213	$	8,568	$	93	$	216	$	15,218
Loans:
Collectively evaluated for impairment	$	403,607	$	112,865	$	129,799	$	393,207	$	8,174	$	19,793	$	1,067,445
Individually evaluated for impairment		1,146		92		—		5,419		100		—		6,757
Balances, end of period	$	404,753	$	112,957	$	129,799	$	398,626	$	8,274	$	19,793	$	1,074,202

December 31, 2017
Allowance for Loan Losses:
Collectively evaluated for impairment	$	3,324	$	1,063	$	1,628	$	7,109	$	91	$	406	$	13,621
Individually evaluated for impairment		—		—		—		100		—		—		100
Balances, end of period	$	3,324	$	1,063	$	1,628	$	7,209	$	91	$	406	$	13,721
Loans:
Collectively evaluated for impairment	$	349,415	$	102,581	$	82,586	$	371,760	$	6,862	$	31,983	$	945,187
Individually evaluated for impairment		1,207		—		—		1,488		—		—		2,695
Balances, end of period	$	350,622	$	102,581	$	82,586	$	373,248	$	6,862	$	31,983	$	947,882

Allocation of ALL with Corresponding Percentage of ALL in Each Category to Total Loans, Net of Deferred Fee

	September 30, 2018					December 31, 2017
	Amount		Percent of total loans, net of deferred fees			Amount		Percent of total loans, net of deferred fees
Commercial real estate	$	3,145		0.29	%	$	3,324		0.35	%
Consumer real estate		983		0.09			1,063		0.11
Construction and land development		2,213		0.21			1,628		0.17
Commercial and industrial		8,568		0.80			7,209		0.77
Consumer		93		0.01			91		0.01
Other		216		0.02			406		0.04
Total allowance for loan losses	$	15,218		1.42	%	$	13,721		1.45	%

Summary of Impaired Loans

The following table presents the Company’s impaired loans that were evaluated for specific loss allowance as of September 30, 2018 and December 31, 2017 (dollars in thousands):


	September 30, 2018						December 31, 2017
	Recorded investment		Unpaid principal balance		Related allowance		Recorded investment		Unpaid principal balance		Related allowance
With no related allowance recorded:
Commercial real estate	$	1,146	$	1,617	$	—	$	1,207	$	1,645	$	—
Consumer real estate		92		92		—		—		—		—
Construction and land development		—		—		—		—		—		—
Commercial and industrial		—		—		—		—		—		—
Consumer		100		100		—		—		—		—
Other		—		—		—		—		—		—
Subtotal		1,338		1,809		—		1,207		1,645		—
With an allowance recorded:
Commercial real estate		—		—		—		—		—		—
Consumer real estate		—		—		—		—		—		—
Construction and land development		—		—		—		—		—		—
Commercial and industrial		5,419		5,419		2,700		1,488		2,770		100
Consumer		—		—		—		—		—		—
Other		—		—		—		—		—		—
Subtotal		5,419		5,419		2,700		1,488		2,770		100
Total	$	6,757	$	7,228	$	2,700	$	2,695	$	4,415	$	100

	Three Months Ended				Three Months Ended				Nine Months Ended				Nine Months Ended
	September 30, 2018				September 30, 2017				September 30, 2018				September 30, 2017
	Average recorded investment		Interest income recognized		Average recorded investment		Interest income recognized		Average recorded investment		Interest income recognized		Average recorded investment		Interest income recognized
With no related allowance recorded:
Commercial real estate	$	1,159	$	15	$	1,245	$	—	$	1,189	$	25	$	1,272	$	—
Consumer real estate		92		—		—		—		92		3		—		—
Construction and land development		—		—		—		—		—		—		—		—
Commercial and industrial		—		—		—		—		—		—		—		—
Consumer		100		—		—		—		100		3		—		—
Other		—		—		—		—		—		—		—		—
Subtotal		1,351		15		1,245		—		1,381		31		1,272		—
With an allowance recorded:
Commercial real estate		—		—		—		—		—		—		—		—
Consumer real estate		—		—		—		—		—		—		—		—
Construction and land development		—		—		—		—		—		—		—		—
Commercial and industrial		5,419		—		1,941		—		5,369		118		2,141		—
Consumer		—		—		—		—		—		—		—		—
Other		—		—		—		—		—		—		—		—
Subtotal		5,419		—		1,941		—		5,369		118		2,141		—
Total	$	6,770	$	15	$	3,186	$	—	$	6,750	$	149	$	3,413	$	—

Schedule of Aging of Recorded Investment in Past-due Loans, by Class of Loans

The following table presents the aging of the recorded investment in past-due loans as of September 30, 2018 and December 31, 2017 by class of loans (dollars in thousands):

	30 - 59		60 - 89		Greater Than
	Days		Days		89 Days		Total		Loans Not
	Past Due		Past Due		Past Due		Past Due		Past Due		Total
September 30, 2018
Commercial real estate	$	2,474	$	—	$	—	$	2,474	$	402,279	$	404,753
Consumer real estate		220		—		215		435		112,522		112,957
Construction and land development		133		—		—		133		129,666		129,799
Commercial and industrial		—		563		4,856		5,419		393,207		398,626
Consumer		—		—		—		—		8,274		8,274
Other		307		—		—		307		19,486		19,793
Total	$	3,134	$	563	$	5,071	$	8,768	$	1,065,434	$	1,074,202

December 31, 2017
Commercial real estate	$	—	$	—	$	—	$	—	$	350,622	$	350,622
Consumer real estate		—		—		218		218		102,363		102,581
Construction and land development		—		—		—		—		82,586		82,586
Commercial and industrial		1,967		209		—		2,176		371,072		373,248
Consumer		—		—		13		13		6,849		6,862
Other		—		—		—		—		31,983		31,983
Total	$	1,967	$	209	$	231	$	2,407	$	945,475	$	947,882

Schedule of Recorded In Non Accrual Loans, Past Due Loans over 89 Days Outstanding and Accruing and Troubled Debt Restructurings

	Non-Accrual		Past Due Over 89 Days and Accruing		Troubled Debt Restructurings
September 30, 2018
Commercial real estate	$	—	$	—	$	1,146
Consumer real estate		92		215		—
Construction and land development		—		—		—
Commercial and industrial		5,419		—		—
Consumer		100		—		—
Other		—		—		—
Total	$	5,611	$	215	$	1,146

December 31, 2017
Commercial real estate	$	1,207	$	—	$	1,207
Consumer real estate		—		218		—
Construction and land development		—		—		—
Commercial and industrial		1,488		—		—
Consumer		—		13		—
Other		—		—		—
Total	$	2,695	$	231	$	1,207

Federal Home Loan Bank Advances (Tables)

9 Months Ended

Sep. 30, 2018

Federal Home Loan Banks [Abstract]

Summary of Contractual Maturities and Average Effective Rates of Outstanding Advances

The following is a summary of the contractual maturities and average effective rates of outstanding advances (dollars in thousands):

	September 30, 2018					December 31, 2017
Year	Amount		Interest Rates			Amount		Interest Rates
2018	$	115,000		2.18	%	$	70,000		1.66	%
2019		10,000		2.45			—		—
2020		—		—			—		—
2021		—		—			—		—
2022		—		—			—		—
Thereafter		—		—			—		—
Total	$	125,000		2.21	%	$	70,000		1.66	%

Accumulated Other Comprehensive Income (Loss) (Tables)

9 Months Ended

Sep. 30, 2018

Accumulated Other Comprehensive Income Loss Net Of Tax [Abstract]

Summary of Changes in Accumulated Other Comprehensive Income (Loss) by Component, Net of Tax

The following were changes in accumulated other comprehensive income (loss) by component, net of tax, for the nine months ended September 30, 2018 and 2017 (dollars in thousands):

				Unrealized Gains			Unrealized
	Gains and			and Losses			Losses on
	Losses on			on Available			Securities
	Cash Flow			for Sale			Transferred to
	Hedges			Securities			Held to Maturity			Total
Nine Months Ended September 30, 2018
Beginning Balance	$	(3,679	)	$	1,162		$	(10	)	$	(2,527	)
Other comprehensive income (loss) before reclassification, net of tax		1,800			(4,521	)		—			(2,721	)
Amounts reclassified from accumulated other comprehensive income (loss), net of tax		(642	)		(1	)		10			(633	)
Net current period other comprehensive income (loss)		1,158			(4,522	)		10			(3,354	)
Ending Balance	$	(2,521	)	$	(3,360	)	$	—		$	(5,881	)

Nine Months Ended September 30, 2017
Beginning Balance	$	(4,241	)	$	(698	)	$	(1,212	)	$	(6,151	)
Other comprehensive income (loss) before reclassification, net of tax		985			1,502			—			2,487
Amounts reclassified from accumulated other comprehensive income (loss), net of tax		(589	)		(26	)		100			(515	)
Net current period other comprehensive income (loss)		396			1,476			100			1,972
Ending Balance	$	(3,845	)	$	778		$	(1,112	)	$	(4,179	)

Summary of Significant Amounts Reclassified out off Accumulated Other Comprehensive Income (Loss)

													Affected Line Item
Details about Accumulated Other	Three Months Ended September 30,						Nine Months Ended September 30,						in the Statement Where
Comprehensive Income Components	2018			2017			2018			2017			Net Income is Presented
Unrealized losses on cash flow hedges	$	(111	)	$	(109	)	$	(330	)	$	(322	)	Interest expense - money market
		(108	)		(168	)		(368	)		(267	)	Interest expense - Federal Home Loan Bank advances
		16			—			56			—		Income tax benefit
	$	(203	)	$	(277	)	$	(642	)	$	(589	)	Net of tax
Unrealized (gains) losses on available- for-sale securities	$	1		$	(9	)	$	(2	)	$	(42	)	Net (gain) loss on sale of securities
		—			3			1			16		Income tax expense
	$	1		$	(6	)	$	(1	)	$	(26	)	Net of tax
Unrealized losses on securities transferred to held-to-maturity	$	—		$	79		$	14		$	162		Interest income - securities
		—			(30	)		(4	)		(62	)	Income tax benefit
	$	—		$	49		$	10		$	100		Net of tax

Commitments and Contingencies (Tables)

9 Months Ended

Sep. 30, 2018

Commitments And Contingencies Disclosure [Abstract]

Schedule of Financial Instruments Representing Credit Risk

The following table sets forth outstanding financial instruments whose contract amounts represent credit risk as of September 30, 2018 and December 31, 2017 (dollars in thousands):

	Contract or notional amount
	September 30, 2018		December 31, 2017
Financial instruments whose contract amounts represent credit risk:
Unused commitments to extend credit	$	622,212	$	584,494
Standby letters of credit		11,526		11,552
Total	$	633,738	$	596,046

- Definition

Tabular disclosure of all significant concentrations of risk, including credit risk and market risk, arising from all financial instruments (as defined), whether from an individual counterparty or groups of counterparties. The disclosure concerning concentrations of risk may consist of the following information: (1) for concentrations of credit risk disclosure may include: (a) information about the (shared) activity, region, or economic characteristic that identifies the concentration, (b) the maximum amount of loss due to credit risk that, based on the gross fair value of the financial instrument, the entity would incur if parties to the financial instruments that make up the concentration failed completely to perform according to the terms of the contracts and the collateral or other security, if any, for the amount due proved to be of no value to the entity, (c) the policy of requiring collateral or other security to support financial instruments subject to credit risk, information about the entity's access to that collateral or other security, and the nature and a brief description of the collateral or other security supporting those financial instruments, and (d) the policy of entering into master netting arrangements to mitigate the credit risk of financial instruments, information about the arrangements for which the entity is a party, and a brief description of the terms of those arrangements, including the extent to which they would reduce the entity's maximum amount of loss due to credit risk and (2) for disclosure of quantitative information about the market risks of financial instruments that is consistent with the way the company manages or adjusts those risks, disclosure may include: (a) more details about current positions and perhaps activity during the period, (b) the hypothetical effects on comprehensive income (or net assets), or annual income, of several possible changes in market prices, (c) a gap analysis of interest rate re-pricing or maturity dates, (d) the duration of the financial instruments, (e) the entity's value at risk from derivatives and from other positions at the end of the reporting period and the average value at risk during the year, or (f) other ways of reporting quantitative information as internally developed.

+ References + Details

Derivatives (Tables)

9 Months Ended

Sep. 30, 2018

Derivative Instruments And Hedging Activities Disclosure [Abstract]

Summary of Interest-Rate Swaps Designated as Cash Flow Hedges

Summary information about the interest-rate swaps designated as cash flow hedges was as follows (dollars in thousands):

	September 30, 2018			December 31, 2017
Notional amounts	$	20,000		$	20,000
Weighted average pay rates		3.54	%		3.54	%
Weighted average receive rates	3 month LIBOR			3 month LIBOR
Weighted average maturity	4.7 years			5.5 years
Fair value	$	(462	)	$	(1,375	)
Amount of unrealized loss recognized in accumulated other comprehensive income, net of tax	$	(341	)	$	(1,016	)

Summary of Customer Related Interest Rate Swaps

A summary of the Company’s customer related interest rate swaps was as follows (dollars in thousands):

	September 30, 2018					December 31, 2017
	Notional		Estimated			Notional		Estimated
	amount		fair value			amount		fair value
Interest rate swap agreements:
Pay fixed/receive variable swaps	$	37,199	$	492		$	41,863	$	55
Pay variable/receive fixed swaps		37,199		(492	)		41,863		(55	)
Total	$	74,398	$	—		$	83,726	$	—

Stock Options and Restricted Shares (Tables)

9 Months Ended

Sep. 30, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Company Recognized Stock-Based Compensation Expense

	Three Months Ended						Nine Months Ended
	September 30,						September 30,
	2018			2017			2018			2017
Stock-based compensation expense before income taxes	$	310		$	288		$	940		$	771
Less: deferred tax benefit		(81	)		(110	)		(246	)		(295	)
Reduction of net income	$	229		$	178		$	694		$	476

Summary of Changes in Company's Nonvested Restricted Shares

A summary of the changes in the Company’s nonvested restricted shares for the nine months ended September 30, 2018 follows:

				Weighted
				Average
	Restricted			Grant Date
Nonvested Shares	Shares			Fair Value
Nonvested at beginning of period		187,253		$	14.21
Granted		53,869			19.11
Vested		(99,603	)		12.61
Forfeited		(8,065	)		15.95
Nonvested at end of period		133,454		$	17.28

Summary of Activity in Stock Options

A summary of the activity in stock options for the nine months ended September 30, 2018 follows:

						Weighted
				Weighted		Average
				Average		Remaining
				Exercise		Contractual
	Shares			Price		Term (years)
Outstanding at beginning of period		804,800		$	10.59
Granted		—			—
Exercised		(508,834	)		10.11
Forfeited or expired		—			—
Outstanding at end of period		295,966		$	11.43		4.0
Fully vested and expected to vest		294,134		$	11.42		3.7
Exercisable at end of period		268,466		$	11.34		3.7

Information Related to Stock Options

Information related to stock options during each year follows:

	2018		2017
Intrinsic value of options exercised	$	4,282,055	$	684,275
Cash received from option exercises		5,144,090		821,500
Tax benefit realized from option exercises		1,119,329		263,446
Weighted average fair value of options granted		—		—

Regulatory Capital Requirements (Tables)

9 Months Ended

Sep. 30, 2018

Banking And Thrift [Abstract]

Schedule of Capital Amounts and Ratios

The Company’s and the Bank’s capital amounts and ratios as of September 30, 2018 and December 31, 2017 are presented in the following table (dollars in thousands).

	Actual					Minimum capital requirement (1)					Minimum to be well-capitalized (2)
	Amount		Ratio			Amount		Ratio			Amount		Ratio
At September 30, 2018:
Total capital to risk-weighted assets:
CapStar Financial Holdings, Inc.	$	171,866		12.62	%	$	108,958		8.00	%	N/A		N/A
CapStar Bank		154,906		11.38			108,897		8.00		$	136,122		10.00
Tier I capital to risk-weighted assets:
CapStar Financial Holdings, Inc.		156,469		11.49			81,718		6.00		N/A		N/A
CapStar Bank		139,509		10.25			81,673		6.00			108,897		8.00
Common equity Tier 1 capital to risk weighted assets:
CapStar Financial Holdings, Inc.		147,469		10.83			61,289		4.50		N/A		N/A
CapStar Bank		123,009		9.04			61,255		4.50			88,479		6.50
Tier I capital to average assets:
CapStar Financial Holdings, Inc.		156,469		11.02			56,770		4.00		N/A		N/A
CapStar Bank		139,509		9.83			56,760		4.00			70,950		5.00

At December 31, 2017:
Total capital to risk-weighted assets:
CapStar Financial Holdings, Inc.	$	156,434		12.52	%	$	99,932		8.00	%	N/A		N/A
CapStar Bank		142,396		11.40			99,928		8.00		$	124,909		10.00
Tier I capital to risk-weighted assets:
CapStar Financial Holdings, Inc.		142,534		11.41			74,949		6.00		N/A		N/A
CapStar Bank		128,496		10.29			74,946		6.00			99,928		8.00
Common equity Tier 1 capital to risk weighted assets:
CapStar Financial Holdings, Inc.		133,703		10.70			56,212		4.50		N/A		N/A
CapStar Bank		112,165		8.98			56,209		4.50			81,191		6.50
Tier I capital to average assets:
CapStar Financial Holdings, Inc.		142,534		10.77			53,218		4.00		N/A		N/A
CapStar Bank		128,496		9.71			53,215		4.00			66,519		5.00

(1)

(2)

Earnings Per Share (Tables)

9 Months Ended

Sep. 30, 2018

Earnings Per Share [Abstract]

Summary of Basic and Diluted Earnings Per Share

The following is a summary of the basic and diluted earnings per share calculation for the three and nine months ended September 30, 2018 and 2017 (dollars in thousands, except share data):

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2018		2017		2018		2017
Basic net income per share calculation:
Numerator – Net income	$	3,656	$	4,419	$	10,363	$	1,409
Denominator – Average common shares outstanding		12,040,229		11,279,364		11,851,476		11,239,093
Basic net income per share	$	0.30	$	0.39	$	0.87	$	0.13
Diluted net income per share calculation:
Numerator – Net income	$	3,656	$	4,419	$	10,363	$	1,409
Denominator – Average common shares outstanding		12,040,229		11,279,364		11,851,476		11,239,093
Dilutive shares contingently issuable		1,073,546		1,471,059		1,201,282		1,518,998
Average diluted common shares outstanding		13,113,775		12,750,423		13,052,758		12,758,091
Diluted net income per share	$	0.28	$	0.35	$	0.79	$	0.11

Fair Value (Tables)

9 Months Ended

Sep. 30, 2018

Fair Value Disclosures [Abstract]

Summary of Assets and Liabilities Measured at Fair Value on a Recurring Basis

Assets and liabilities measured at fair value on a recurring basis are summarized below (dollars in thousands):

	Fair value measurements at September 30, 2018
				Quoted prices
				in active		Significant
				markets for		other			Significant
				identical		observable			unobservable
	Carrying			assets		inputs			inputs
	Value			(Level 1)		(Level 2)			(Level 3)
Assets:
Securities available-for-sale:
U.S. government-sponsored agencies	$	10,465		$	—	$	10,465		$	—
Obligations of states and political subdivisions		44,245			—		44,245			—
Mortgage-backed securities-residential		105,202			—		105,202			—
Asset-backed securities		15,713			—		15,713			—
Other debt securities		11,844			—		11,844			—
Total securities available-for-sale	$	187,469		$	—	$	187,469		$	—
Derivatives:
Interest rate swaps - customer related	$	624		$	—	$	624		$	—
Liabilities:
Derivatives:
Interest rate swaps - customer related	$	(624	)	$	—	$	(624	)	$	—
Interest rate swaps - cash flow hedges		(462	)		—		(462	)		—
Total derivatives	$	(1,086	)	$	—	$	(1,086	)	$	—

	Fair value measurements at December 31, 2017
				Quoted prices
				in active		Significant
				markets for		other			Significant
				identical		observable			unobservable
	Carrying			assets		inputs			inputs
	Value			(Level 1)		(Level 2)			(Level 3)
Assets:
Securities available-for-sale:
U.S. government-sponsored agencies	$	11,277		$	—	$	11,277		$	—
Obligations of states and political subdivisions		52,998			—		52,998			—
Mortgage-backed securities-residential		106,562			—		106,562			—
Asset-backed securities		16,377			—		16,377			—
Other debt securities		5,407			—		5,407			—
Total securities available-for-sale	$	192,621		$	—	$	192,621		$	—
Derivatives:
Interest rate swaps - customer related	$	184		$	—	$	184		$	—
Liabilities:
Derivatives:
Interest rate swaps - customer related	$	(184	)	$	—	$	(184	)	$	—
Interest rate swaps - cash flow hedges		(1,375	)		—		(1,375	)		—
Total derivatives	$	(1,559	)	$	—	$	(1,559	)	$	—

Summary of Assets Measured at Fair Value on a Nonrecurring Basis

Assets measured at fair value on a nonrecurring basis are summarized below (dollars in thousands):

Fair value measurements at September 30, 2018

Quoted prices

in active

Significant

markets for

other

Significant

identical

observable

unobservable

Carrying

assets

inputs

Value

(level 1)

(level 2)

(level 3)

Assets:

Impaired loans:

Commercial and industrial

2,719

—

2,719

Fair value measurements at December 31, 2017

Quoted prices

in active

Significant

markets for

other

Significant

identical

observable

unobservable

Carrying

assets

inputs

Value

(level 1)

(level 2)

(level 3)

Assets:

Impaired loans:

Commercial and industrial

1,388

—

1,388

Summary of Quantitative Information About Level 3 Fair Value Measurements for Assets Measured at Fair Value on a Non-recurring Basis

					Range
	Fair		Valuation		(Weighted-
September 30, 2018	Value		Technique(s)	Unobservable Input(s)	Average)
Impaired loans:
Commercial and industrial	$	2,719	Discounted cash flow	Probability of default	5%-60%
				Loss severity	5%-50%

Range

Fair

Valuation

(Weighted-

December 31, 2017

Value

Technique(s)

Unobservable Input(s)

Average)

Impaired loans:

Commercial and industrial

1,388

Sales comparison approach

Appraisal discounts

Summary of Carrying Value and Fair Values of the Bank's Financial Instruments

The carrying value and estimated fair values of the Bank’s financial instruments at September 30, 2018 and December 31, 2017 were as follows (dollars in thousands):

	September 30, 2018				December 31, 2017
	Carrying				Carrying				Fair value
	amount		Fair value		amount		Fair value		level of input
Financial assets:
Cash and due from banks, interest-bearing deposits in financial institutions	$	49,842	$	49,842	$	78,078	$	78,078	Level 1
Federal funds sold		2,747		2,747		4,719		4,719	Level 1
Securities available-for-sale		187,469		187,469		192,621		192,621	Level 2
Securities held-to-maturity		3,740		3,766		3,759		3,848	Level 2
Loans held for sale		50,499		51,326		74,093		75,549	Level 2
Restricted equity securities		8,817	N/A			8,806	N/A		N/A
Loans, net		1,073,870		1,065,226		947,537		944,037	Level 3
Accrued interest receivable		4,430		4,430		4,084		4,084	Level 2
Other assets		23,519		23,519		22,663		22,663	Level 2
Financial liabilities:
Deposits		1,126,403		1,074,725		1,119,866		1,065,669	Level 3
Federal Home Loan Bank advances		125,000		124,983		70,000		69,980	Level 2
Other liabilities		2,447		2,447		3,672		3,672	Level 3

Securities - Summary of Fair Value of Available for Sale Held to Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Securities available for sale [Abstract]
Amortized Cost	$ 194,330	$ 193,360
Gross unrealized gains	280	1,563
Gross unrealized (losses)	(7,141)	(2,302)
Estimated fair value	187,469	192,621
Securities held to maturity [Abstract]
Amortized Cost	3,740	3,759
Gross unrealized gains	31	89
Gross unrealized (losses)	(5)
Estimated fair value	3,766	3,848
U. S. government agency securities
Securities available for sale [Abstract]
Amortized Cost	11,054	11,433
Gross unrealized gains		12
Gross unrealized (losses)	(589)	(168)
Estimated fair value	10,465	11,277
State and municipal securities
Securities available for sale [Abstract]
Amortized Cost	45,738	51,790
Gross unrealized gains	228	1,430
Gross unrealized (losses)	(1,721)	(222)
Estimated fair value	44,245	52,998
Securities held to maturity [Abstract]
Amortized Cost	3,740	3,759
Gross unrealized gains	31	89
Gross unrealized (losses)	(5)
Estimated fair value	3,766	3,848
Mortgage-backed securities
Securities available for sale [Abstract]
Amortized Cost	109,983	108,236
Gross unrealized gains		40
Gross unrealized (losses)	(4,781)	(1,714)
Estimated fair value	105,202	106,562
Asset-backed securities
Securities available for sale [Abstract]
Amortized Cost	15,687	16,575
Gross unrealized gains	26
Gross unrealized (losses)		(198)
Estimated fair value	15,713	16,377
Other debt securities
Securities available for sale [Abstract]
Amortized Cost	11,868	5,326
Gross unrealized gains	26	81
Gross unrealized (losses)	(50)
Estimated fair value	$ 11,844	$ 5,407

Securities - Summary of Securities with Unrealized Losses and Length of Time Continuous Loss Positions (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Available-for-sale securities, continuous unrealized loss position [Abstract]
Less than 12 months, Estimated fair value	$ 67,729	$ 44,697
Less than 12 months, Gross unrealized (losses)	(2,131)	(518)
12 months or more, Estimated fair value	89,320	91,900
12 months or more, Gross unrealized losses	(5,015)	(1,784)
Total, Estimated fair value	157,049	136,597
Total, Gross unrealized losses	(7,146)	(2,302)
U. S. government agency securities
Available-for-sale securities, continuous unrealized loss position [Abstract]
Less than 12 months, Estimated fair value	1,827	7,375
Less than 12 months, Gross unrealized (losses)	(76)	(90)
12 months or more, Estimated fair value	8,638	1,912
12 months or more, Gross unrealized losses	(513)	(78)
Total, Estimated fair value	10,465	9,287
Total, Gross unrealized losses	(589)	(168)
State and municipal securities
Available-for-sale securities, continuous unrealized loss position [Abstract]
Less than 12 months, Estimated fair value	28,333	7,490
Less than 12 months, Gross unrealized (losses)	(1,134)	(106)
12 months or more, Estimated fair value	7,531	5,798
12 months or more, Gross unrealized losses	(592)	(116)
Total, Estimated fair value	35,864	13,288
Total, Gross unrealized losses	(1,726)	(222)
Mortgage-backed securities
Available-for-sale securities, continuous unrealized loss position [Abstract]
Less than 12 months, Estimated fair value	32,051	29,832
Less than 12 months, Gross unrealized (losses)	(871)	(322)
12 months or more, Estimated fair value	73,151	67,813
12 months or more, Gross unrealized losses	(3,910)	(1,392)
Total, Estimated fair value	105,202	97,645
Total, Gross unrealized losses	(4,781)	(1,714)
Asset-backed securities
Available-for-sale securities, continuous unrealized loss position [Abstract]
12 months or more, Estimated fair value		16,377
12 months or more, Gross unrealized losses		(198)
Total, Estimated fair value		16,377
Total, Gross unrealized losses		$ (198)
Other debt securities
Available-for-sale securities, continuous unrealized loss position [Abstract]
Less than 12 months, Estimated fair value	5,518
Less than 12 months, Gross unrealized (losses)	(50)
Total, Estimated fair value	5,518
Total, Gross unrealized losses	$ (50)

Securities - Additional Information (Details) $ in Millions	Sep. 30, 2018 USD ($)
Schedule Of Available For Sale Securities [Line Items]
Unrealized losses in investment securities portfolio	$ 7.1
Public Deposits, Derivative Positions and Federal Home Loan Bank Advances
Schedule Of Available For Sale Securities [Line Items]
Carrying value of securities	$ 148.7

Securities - Summary of Sale of Debt and Equity Securities (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Investments Debt And Equity Securities [Abstract]
Proceeds	$ 5,778	$ 34,299
Gross gains	107	99
Gross losses	$ (105)	$ (57)

Securities - Summary of Amortized Cost and Fair Value of Debt and Equity Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Available-for-sale, Amortized cost [Abstract]
Due in less than one year	$ 1,763
Due one to five years	21,080
Due five to ten years	28,383
Due beyond ten years	17,434
Amortized Cost	194,330	$ 193,360
Available-for-sale, Estimated fair value [Abstract]
Due in less than one year	1,756
Due one to five years	21,095
Due five to ten years	27,302
Due beyond ten years	16,401
Total	187,469	192,621
Held-to-maturity, Amortized cost [Abstract]
Due in less than one year	394
Due one to five years	3,346
Amortized Cost	3,740	3,759
Securities held to maturity [Abstract]
Due in less than one year	396
Due one to five years	3,370
Total	3,766	3,848
Mortgage-backed securities
Available-for-sale, Amortized cost [Abstract]
Amortized cost	109,983
Amortized Cost	109,983	108,236
Available-for-sale, Estimated fair value [Abstract]
Estimated fair value	105,202
Total	105,202	106,562
Asset-backed securities
Available-for-sale, Amortized cost [Abstract]
Amortized cost	15,687
Amortized Cost	15,687	16,575
Available-for-sale, Estimated fair value [Abstract]
Estimated fair value	15,713
Total	$ 15,713	$ 16,377

Loans and Allowance for Loan Losses - Summary of Loan Portfolio (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016
Loans And Leases Receivable Disclosure [Line Items]
Total loans	$ 1,074,202		$ 947,882
Less net unearned income	(332)		(345)
Total loans	1,073,870		947,537
Less allowance for loan losses	(15,218)	$ (14,705)	(13,721)	$ (14,122)	$ (12,454)	$ (11,634)
Loans, net	1,058,652		933,816
Commercial real estate
Loans And Leases Receivable Disclosure [Line Items]
Total loans	404,753		350,622
Less allowance for loan losses	(3,145)	(3,551)	(3,324)	(3,294)	(3,533)	(2,655)
Consumer real estate
Loans And Leases Receivable Disclosure [Line Items]
Total loans	112,957		102,581
Less allowance for loan losses	(983)	(1,057)	(1,063)	(984)	(1,081)	(1,013)
Construction and land development
Loans And Leases Receivable Disclosure [Line Items]
Total loans	129,799		82,586
Less allowance for loan losses	(2,213)	(1,764)	(1,628)	(1,487)	(911)	(1,574)
Commercial and industrial
Loans And Leases Receivable Disclosure [Line Items]
Total loans	398,626		373,248
Less allowance for loan losses	(8,568)	(7,779)	(7,209)	(7,949)	(6,395)	(5,618)
Consumer
Loans And Leases Receivable Disclosure [Line Items]
Total loans	8,274		6,862
Less allowance for loan losses	(93)	(120)	(91)	(79)	(57)	(76)
Other
Loans And Leases Receivable Disclosure [Line Items]
Total loans	19,793		31,983
Less allowance for loan losses	$ (216)	$ (434)	$ (406)	$ (329)	$ (477)	$ (698)

Loans and Allowance for Loan Losses - Additional Information (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) Contract	Sep. 30, 2017 USD ($) Contract	Sep. 30, 2018 USD ($) Contract	Sep. 30, 2017 USD ($) Contract	Dec. 31, 2017 USD ($)
Loans And Leases Receivable Disclosure [Line Items]
Minimum loan amount for loans analyzed by credit risk			$ 500,000
Total loans	$ 1,074,202,000		1,074,202,000		$ 947,882,000
Interest income recognized on a cash basis for impaired loans	15,000	$ 0	25,000	$ 0
Investment in TDR	1,100,000		1,100,000		1,100,000
Specific allowance related to loans	2,700,000		2,700,000		100,000
Additional commitments related to TDR	$ 0		$ 0		0
New TDR identified during the period \| Contract	0	0	0	0
TDR, payment default within twelve months \| Contract	0	0	0	0
Loan period considered as payment default			30 days
Troubled Debt Restructurings
Loans And Leases Receivable Disclosure [Line Items]
Specific allowance related to loans	$ 0		$ 0		0
Doubtful
Loans And Leases Receivable Disclosure [Line Items]
Total loans	$ 0		$ 0		$ 0

Loans and Allowance for Loan Losses - Summary of Loan Balances by Category as well as Risk Rating (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable Recorded Investment [Line Items]
Total loans	$ 1,074,202	$ 947,882
Total Impaired Loans
Financing Receivable Recorded Investment [Line Items]
Total loans	6,757	2,695
Non Impaired Loans
Financing Receivable Recorded Investment [Line Items]
Total loans	1,067,445	945,187
Non Impaired Loans \| Pass Watch
Financing Receivable Recorded Investment [Line Items]
Total loans	1,052,106	922,898
Non Impaired Loans \| Special Mention
Financing Receivable Recorded Investment [Line Items]
Total loans	6,992	11,193
Non Impaired Loans \| Substandard
Financing Receivable Recorded Investment [Line Items]
Total loans	8,347	11,096
Commercial real estate
Financing Receivable Recorded Investment [Line Items]
Total loans	404,753	350,622
Commercial real estate \| Total Impaired Loans
Financing Receivable Recorded Investment [Line Items]
Total loans	1,146	1,207
Commercial real estate \| Non Impaired Loans
Financing Receivable Recorded Investment [Line Items]
Total loans	403,607	349,415
Commercial real estate \| Non Impaired Loans \| Pass Watch
Financing Receivable Recorded Investment [Line Items]
Total loans	402,254	349,415
Commercial real estate \| Non Impaired Loans \| Substandard
Financing Receivable Recorded Investment [Line Items]
Total loans	1,353
Consumer real estate
Financing Receivable Recorded Investment [Line Items]
Total loans	112,957	102,581
Consumer real estate \| Total Impaired Loans
Financing Receivable Recorded Investment [Line Items]
Total loans	92
Consumer real estate \| Non Impaired Loans
Financing Receivable Recorded Investment [Line Items]
Total loans	112,865	102,581
Consumer real estate \| Non Impaired Loans \| Pass Watch
Financing Receivable Recorded Investment [Line Items]
Total loans	112,640	102,571
Consumer real estate \| Non Impaired Loans \| Substandard
Financing Receivable Recorded Investment [Line Items]
Total loans	225	10
Construction and land development
Financing Receivable Recorded Investment [Line Items]
Total loans	129,799	82,586
Construction and land development \| Non Impaired Loans
Financing Receivable Recorded Investment [Line Items]
Total loans	129,799	82,586
Construction and land development \| Non Impaired Loans \| Pass Watch
Financing Receivable Recorded Investment [Line Items]
Total loans	129,799	82,586
Commercial and industrial
Financing Receivable Recorded Investment [Line Items]
Total loans	398,626	373,248
Commercial and industrial \| Total Impaired Loans
Financing Receivable Recorded Investment [Line Items]
Total loans	5,419	1,488
Commercial and industrial \| Non Impaired Loans
Financing Receivable Recorded Investment [Line Items]
Total loans	393,207	371,760
Commercial and industrial \| Non Impaired Loans \| Pass Watch
Financing Receivable Recorded Investment [Line Items]
Total loans	379,446	349,494
Commercial and industrial \| Non Impaired Loans \| Special Mention
Financing Receivable Recorded Investment [Line Items]
Total loans	6,992	11,193
Commercial and industrial \| Non Impaired Loans \| Substandard
Financing Receivable Recorded Investment [Line Items]
Total loans	6,769	11,073
Consumer
Financing Receivable Recorded Investment [Line Items]
Total loans	8,274	6,862
Consumer \| Total Impaired Loans
Financing Receivable Recorded Investment [Line Items]
Total loans	100
Consumer \| Non Impaired Loans
Financing Receivable Recorded Investment [Line Items]
Total loans	8,174	6,862
Consumer \| Non Impaired Loans \| Pass Watch
Financing Receivable Recorded Investment [Line Items]
Total loans	8,174	6,849
Consumer \| Non Impaired Loans \| Substandard
Financing Receivable Recorded Investment [Line Items]
Total loans		13
Other
Financing Receivable Recorded Investment [Line Items]
Total loans	19,793	31,983
Other \| Non Impaired Loans
Financing Receivable Recorded Investment [Line Items]
Total loans	19,793	31,983
Other \| Non Impaired Loans \| Pass Watch
Financing Receivable Recorded Investment [Line Items]
Total loans	$ 19,793	$ 31,983

Loans and Allowance for Loan Losses - Summary of Changes in Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning Balance	$ 14,705	$ 12,454	$ 13,721	$ 11,634
Charged-off loans			(251)	(12,369)
Recoveries	32	1,863	420	1,957
Provision for loan losses	481	(195)	1,328	12,900
Ending Balance	15,218	14,122	15,218	14,122
Commercial real estate
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning Balance	3,551	3,533	3,324	2,655
Recoveries	6	3	16	4
Provision for loan losses	(412)	(242)	(195)	635
Ending Balance	3,145	3,294	3,145	3,294
Consumer real estate
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning Balance	1,057	1,081	1,063	1,013
Recoveries	1		4
Provision for loan losses	(75)	(97)	(84)	(29)
Ending Balance	983	984	983	984
Construction and land development
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning Balance	1,764	911	1,628	1,574
Provision for loan losses	449	576	585	(87)
Ending Balance	2,213	1,487	2,213	1,487
Commercial and industrial
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning Balance	7,779	6,395	7,209	5,618
Charged-off loans			(226)	(12,369)
Recoveries	22	1,860	348	1,862
Provision for loan losses	767	(306)	1,237	12,838
Ending Balance	8,568	7,949	8,568	7,949
Consumer
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning Balance	120	57	91	76
Charged-off loans			(25)
Recoveries	3		52	91
Provision for loan losses	(30)	22	(25)	(88)
Ending Balance	93	79	93	79
Other
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning Balance	434	477	406	698
Provision for loan losses	(218)	(148)	(190)	(369)
Ending Balance	$ 216	$ 329	$ 216	$ 329

Loans and Allowance for Loan Losses - Summary of Breakdown of Allowance for Loan Losses and Loan Portfolio by Loan Category (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016
Allowance for Loan Losses:
Collectively evaluated for impairment	$ 12,518		$ 13,621
Individually evaluated for impairment	2,700		100
Allowance for Loan Losses, Ending Balance	15,218	$ 14,705	13,721	$ 14,122	$ 12,454	$ 11,634
Loans:
Collectively evaluated for impairment	1,067,445		945,187
Individually evaluated for impairment	6,757		2,695
Total	1,074,202		947,882
Commercial real estate
Allowance for Loan Losses:
Collectively evaluated for impairment	3,145		3,324
Allowance for Loan Losses, Ending Balance	3,145	3,551	3,324	3,294	3,533	2,655
Loans:
Collectively evaluated for impairment	403,607		349,415
Individually evaluated for impairment	1,146		1,207
Total	404,753		350,622
Consumer real estate
Allowance for Loan Losses:
Collectively evaluated for impairment	983		1,063
Allowance for Loan Losses, Ending Balance	983	1,057	1,063	984	1,081	1,013
Loans:
Collectively evaluated for impairment	112,865		102,581
Individually evaluated for impairment	92
Total	112,957		102,581
Construction and land development
Allowance for Loan Losses:
Collectively evaluated for impairment	2,213		1,628
Allowance for Loan Losses, Ending Balance	2,213	1,764	1,628	1,487	911	1,574
Loans:
Collectively evaluated for impairment	129,799		82,586
Total	129,799		82,586
Commercial and industrial
Allowance for Loan Losses:
Collectively evaluated for impairment	5,868		7,109
Individually evaluated for impairment	2,700		100
Allowance for Loan Losses, Ending Balance	8,568	7,779	7,209	7,949	6,395	5,618
Loans:
Collectively evaluated for impairment	393,207		371,760
Individually evaluated for impairment	5,419		1,488
Total	398,626		373,248
Consumer
Allowance for Loan Losses:
Collectively evaluated for impairment	93		91
Allowance for Loan Losses, Ending Balance	93	120	91	79	57	76
Loans:
Collectively evaluated for impairment	8,174		6,862
Individually evaluated for impairment	100
Total	8,274		6,862
Other
Allowance for Loan Losses:
Collectively evaluated for impairment	216		406
Allowance for Loan Losses, Ending Balance	216	$ 434	406	$ 329	$ 477	$ 698
Loans:
Collectively evaluated for impairment	19,793		31,983
Total	$ 19,793		$ 31,983

Loans and Allowance for Loan Losses - Allocation of ALL with Corresponding Percentage of ALL in Each Category to Total Loans, Net of Deferred Fee (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016
Loans And Leases Receivable Disclosure [Line Items]
Allowance for loan losses, Amount	$ 15,218	$ 14,705	$ 13,721	$ 14,122	$ 12,454	$ 11,634
Allowance for loan losses, Percentage of total loans, net of deferred fees	1.42%		1.45%
Commercial real estate
Loans And Leases Receivable Disclosure [Line Items]
Allowance for loan losses, Amount	$ 3,145	3,551	$ 3,324	3,294	3,533	2,655
Allowance for loan losses, Percentage of total loans, net of deferred fees	0.29%		0.35%
Consumer real estate
Loans And Leases Receivable Disclosure [Line Items]
Allowance for loan losses, Amount	$ 983	1,057	$ 1,063	984	1,081	1,013
Allowance for loan losses, Percentage of total loans, net of deferred fees	0.09%		0.11%
Construction and land development
Loans And Leases Receivable Disclosure [Line Items]
Allowance for loan losses, Amount	$ 2,213	1,764	$ 1,628	1,487	911	1,574
Allowance for loan losses, Percentage of total loans, net of deferred fees	0.21%		0.17%
Commercial and industrial
Loans And Leases Receivable Disclosure [Line Items]
Allowance for loan losses, Amount	$ 8,568	7,779	$ 7,209	7,949	6,395	5,618
Allowance for loan losses, Percentage of total loans, net of deferred fees	0.80%		0.77%
Consumer
Loans And Leases Receivable Disclosure [Line Items]
Allowance for loan losses, Amount	$ 93	120	$ 91	79	57	76
Allowance for loan losses, Percentage of total loans, net of deferred fees	0.01%		0.01%
Other
Loans And Leases Receivable Disclosure [Line Items]
Allowance for loan losses, Amount	$ 216	$ 434	$ 406	$ 329	$ 477	$ 698
Allowance for loan losses, Percentage of total loans, net of deferred fees	0.02%		0.04%

Loans and Allowance for Loan Losses - Summary of Impaired Loans Evaluated for Specific Loss Allowance (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable Impaired [Line Items]
Impaired loans with no related allowance recorded, Recorded investment	$ 1,338	$ 1,207
Impaired loans with no related allowance recorded, Unpaid principal balance	1,809	1,645
Impaired loans with an allowance recorded, Related allowance	2,700	100
Impaired loans with an allowance recorded, Recorded investment	5,419	1,488
Impaired loans with an allowance recorded, Unpaid principal balance	5,419	2,770
Recorded investment	6,757	2,695
Unpaid principal balance	7,228	4,415
Commercial real estate
Financing Receivable Impaired [Line Items]
Impaired loans with no related allowance recorded, Recorded investment	1,146	1,207
Impaired loans with no related allowance recorded, Unpaid principal balance	1,617	1,645
Consumer real estate
Financing Receivable Impaired [Line Items]
Impaired loans with no related allowance recorded, Recorded investment	92
Impaired loans with no related allowance recorded, Unpaid principal balance	92
Commercial and industrial
Financing Receivable Impaired [Line Items]
Impaired loans with an allowance recorded, Related allowance	2,700	100
Impaired loans with an allowance recorded, Recorded investment	5,419	1,488
Impaired loans with an allowance recorded, Unpaid principal balance	5,419	$ 2,770
Consumer
Financing Receivable Impaired [Line Items]
Impaired loans with no related allowance recorded, Recorded investment	100
Impaired loans with no related allowance recorded, Unpaid principal balance	$ 100

Loans and Allowance for Loan Losses - Summary of Average Recorded Investment and Interest Income Recognized on Impaired Loans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Financing Receivable Impaired [Line Items]
Impaired loans with no related allowance recorded, Average recorded investment	$ 1,351	$ 1,245	$ 1,381	$ 1,272
Impaired loans with no related allowance recorded, Interest income recognized	15		31
Impaired loans with an allowance recorded, Average recorded investment	5,419	1,941	5,369	2,141
Impaired loans with an allowance recorded, Interest income recognized			118
Average recorded investment	6,770	3,186	6,750	3,413
Interest income recognized	15		149
Commercial real estate
Financing Receivable Impaired [Line Items]
Impaired loans with no related allowance recorded, Average recorded investment	1,159	1,245	1,189	1,272
Impaired loans with no related allowance recorded, Interest income recognized	15		25
Consumer real estate
Financing Receivable Impaired [Line Items]
Impaired loans with no related allowance recorded, Average recorded investment	92		92
Impaired loans with no related allowance recorded, Interest income recognized			3
Commercial and industrial
Financing Receivable Impaired [Line Items]
Impaired loans with an allowance recorded, Average recorded investment	5,419	$ 1,941	5,369	$ 2,141
Impaired loans with an allowance recorded, Interest income recognized			118
Consumer
Financing Receivable Impaired [Line Items]
Impaired loans with no related allowance recorded, Average recorded investment	$ 100		100
Impaired loans with no related allowance recorded, Interest income recognized			$ 3

Loans and Allowance for Loan Losses - Schedule of Aging of Recorded Investment in Past-due Loans, by Class of Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	$ 8,768	$ 2,407
Loans Not Past Due	1,065,434	945,475
Total	1,074,202	947,882
Commercial real estate
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	2,474
Loans Not Past Due	402,279	350,622
Total	404,753	350,622
Consumer real estate
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	435	218
Loans Not Past Due	112,522	102,363
Total	112,957	102,581
Construction and land development
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	133
Loans Not Past Due	129,666	82,586
Total	129,799	82,586
Commercial and industrial
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	5,419	2,176
Loans Not Past Due	393,207	371,072
Total	398,626	373,248
Consumer
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		13
Loans Not Past Due	8,274	6,849
Total	8,274	6,862
Other
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	307
Loans Not Past Due	19,486	31,983
Total	19,793	31,983
30 - 59 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	3,134	1,967
30 - 59 Days Past Due [Member] \| Commercial real estate
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	2,474
30 - 59 Days Past Due [Member] \| Consumer real estate
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	220
30 - 59 Days Past Due [Member] \| Construction and land development
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	133
30 - 59 Days Past Due [Member] \| Commercial and industrial
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		1,967
30 - 59 Days Past Due [Member] \| Other
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	307
60 - 89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	563	209
60 - 89 Days Past Due [Member] \| Commercial and industrial
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	563	209
Greater than 89 Days Past Due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	5,071	231
Greater than 89 Days Past Due [Member] \| Consumer real estate
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	215	218
Greater than 89 Days Past Due [Member] \| Commercial and industrial
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	$ 4,856
Greater than 89 Days Past Due [Member] \| Consumer
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due		$ 13

Loans and Allowance for Loan Losses - Schedule of Non-Accrual Loans, Past Due Loans over 89 Days Outstanding and Accruing and Troubled Debt Restructurings (TDR) by Class of Loans (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Accounts Notes And Loans Receivable [Line Items]
Non-Accrual	$ 5,611	$ 2,695
Past Due Over 89 Days and Accruing	215	231
Troubled Debt Restructurings	1,146	1,207
Commercial real estate
Accounts Notes And Loans Receivable [Line Items]
Non-Accrual		1,207
Troubled Debt Restructurings	1,146	1,207
Consumer real estate
Accounts Notes And Loans Receivable [Line Items]
Non-Accrual	92
Past Due Over 89 Days and Accruing	215	218
Commercial and industrial
Accounts Notes And Loans Receivable [Line Items]
Non-Accrual	5,419	1,488
Consumer
Accounts Notes And Loans Receivable [Line Items]
Non-Accrual	$ 100
Past Due Over 89 Days and Accruing		$ 13

Federal Home Loan Bank Advances - Additional Information (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Federal Home Loan Bank Advances [Line Items]
Outstanding borrowings	$ 125,000	$ 70,000
Investment securities, FHLB stock and commercial and residential real estate mortgage loans
Federal Home Loan Bank Advances [Line Items]
Federal Home Loan Bank Advances Collateralized Investment Securities Value	3,900
Mortgage loans collateralized amount	420,600
Amount of available credit	$ 59,400

Federal Home Loan Bank Advances - Summary of Contractual Maturities and Average Effective Rates of Outstanding Advances (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Federal Home Loan Bank Advances Maturities Summary [Abstract]
2018	$ 115,000	$ 70,000
2019	10,000
Total amount	$ 125,000	$ 70,000
2018	2.18%	1.66%
2019	2.45%
Total interest rates	2.21%	1.66%

Accumulated Other Comprehensive Income (Loss) - Summary of Changes In Accumulated Other Comprehensive Income (Loss) By Component, Net of Tax (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance			$ 146,946	$ 139,207
Other comprehensive income (loss) before reclassification, net of tax			(2,721)	2,487
Amounts reclassified from accumulated other comprehensive income (loss), net of tax			(633)	(515)
Net current period other comprehensive income (loss)	$ (577)	$ 583	(3,354)	1,972
Ending balance	157,510	144,204	157,510	144,204
Gains and Losses on Cash Flow Hedges
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance			(3,679)	(4,241)
Other comprehensive income (loss) before reclassification, net of tax			1,800	985
Amounts reclassified from accumulated other comprehensive income (loss), net of tax			(642)	(589)
Net current period other comprehensive income (loss)			1,158	396
Ending balance	(2,521)	(3,845)	(2,521)	(3,845)
Unrealized Gains and Losses on Available for Sale Securities
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance			1,162	(698)
Other comprehensive income (loss) before reclassification, net of tax			(4,521)	1,502
Amounts reclassified from accumulated other comprehensive income (loss), net of tax			(1)	(26)
Net current period other comprehensive income (loss)			(4,522)	1,476
Ending balance	(3,360)	778	(3,360)	778
Unrealized Losses on Securities Transferred to Held to Maturity
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance			(10)	(1,212)
Amounts reclassified from accumulated other comprehensive income (loss), net of tax			10	100
Net current period other comprehensive income (loss)			10	100
Ending balance		(1,112)		(1,112)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance			(2,527)	(6,151)
Net current period other comprehensive income (loss)			(3,354)	1,972
Ending balance	$ (5,881)	$ (4,179)	$ (5,881)	$ (4,179)

Accumulated Other Comprehensive Income (Loss) - Summary of Significant Amounts Reclassified out of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Net (gain) loss on sale of securities			$ 2	$ 42
Interest expense - Federal Home Loan Bank advances	$ (698)	$ (563)	(1,813)	(1,083)
Income tax benefit	(554)	(1,516)	(1,702)	(141)
Net income	3,656	4,419	10,363	1,409
Reclassification out of Accumulated Other Comprehensive Income \| Unrealized Losses on Cash Flow Hedges
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Interest expense money market	(111)	(109)	(330)	(322)
Interest expense - Federal Home Loan Bank advances	(108)	(168)	(368)	(267)
Income tax benefit	16		56
Net income	(203)	(277)	(642)	(589)
Reclassification out of Accumulated Other Comprehensive Income \| Unrealized Gains and Losses on Available for Sale Securities
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Net (gain) loss on sale of securities	1	(9)	(2)	(42)
Income tax benefit		3	1	16
Net income	$ 1	(6)	(1)	(26)
Reclassification out of Accumulated Other Comprehensive Income \| Unrealized Losses on Securities Transferred to Held to Maturity
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Interest income - securities		79	14	162
Income tax benefit		(30)	(4)	(62)
Net income		$ 49	$ 10	$ 100

Income Taxes - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Income Taxes [Line Items]
Effective tax rate	13.20%	25.50%	14.10%	9.10%
Income tax expense	$ (422,000)	$ (144,000)	$ (1,062,000)	$ (310,000)
Federal statutory income tax rate			21.00%		35.00%
Tennessee \| State and Local Jurisdiction
Income Taxes [Line Items]
Excise tax rate			6.50%

Commitments and Contingencies - Schedule of Financial Instruments Representing Credit Risk (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Unused commitments to extend credit	$ 622,212	$ 584,494
Standby letters of credit	11,526	11,552
Total	$ 633,738	$ 596,046

Derivatives - Additional Information (Details) - Designated as Hedging Instrument - Interest Rate Swaps - Cash Flow Hedges - USD ($)	Sep. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Notional amounts	$ 20,000,000	$ 20,000,000
Investment securities pledged collateral to counterparties	2,100,000
Investment securities pledged collateral from counterparties	$ 0

Derivatives - Summary of Interest-Rate Swaps Designated as Cash Flow Hedges (Details) - Designated as Hedging Instrument - Cash Flow Hedges - Interest Rate Swaps - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Notional amounts	$ 20,000,000	$ 20,000,000
Weighted average pay rates	3.54%	3.54%
Weighted average receive rates	September 30, 2018: 3 month LIBOR and Dec. 31, 2017: 3 month LIBOR
Weighted average maturity	4 years 8 months 12 days	5 years 6 months
Fair value	$ (462,000)	$ (1,375,000)
Amount of unrealized loss recognized in accumulated other comprehensive income, net of tax	$ (341,000)	$ (1,016,000)

Derivatives - Summary of Customer Related Interest Rate Swaps (Details) - Interest Rate Swaps - USD ($)	Sep. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Interest rate swap, Notional amount	$ 74,398,000	$ 83,726,000
Pay fixed/receive variable swaps
Derivative [Line Items]
Interest rate swap, Notional amount	37,199,000	41,863,000
Interest rate swap, Estimated fair value	492,000	55,000
Pay variable/receive fixed swaps
Derivative [Line Items]
Interest rate swap, Notional amount	37,199,000	41,863,000
Interest rate swap, Estimated fair value	$ (492,000)	$ (55,000)

Stock Options and Restricted Shares - Additional Information (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Apr. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation cost	$ 1.6
Total fair value of shares vested	$ 1.9	$ 1.1
Vesting period	4 years
Contractual term	10 years
Options granted	0	0
Unrecognized compensation cost	$ 0.1
Restricted Shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Cost expected to be recognized over a weighted-average period	2 years
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Cost expected to be recognized over a weighted-average period	1 year
CapStar Bank 2008 Stock Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares of stock reserved for issuance of stock incentives	1,569,475		400,000
Shares issuable under both restricted share and stock option grants	506,435

Stock Options and Restricted Shares - Summary of Company Recognized Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-based compensation expense before income taxes	$ 310	$ 288	$ 940	$ 771
Less: deferred tax benefit	(81)	(110)	(246)	(295)
Reduction of net income	$ 229	$ 178	$ 694	$ 476

Stock Options and Restricted Shares - Summary of Changes in Company's Nonvested Restricted Shares (Details)	9 Months Ended
	Sep. 30, 2018 $ / shares shares
Restricted Shares, Abstract
Restricted Shares, Nonvested Beginning Balance \| shares	187,253
Restricted Shares, Granted \| shares	53,869
Restricted Shares, Vested \| shares	(99,603)
Restricted Shares, Forfeited \| shares	(8,065)
Restricted Shares, Nonvested Ending Balance \| shares	133,454
Weighted Average Grant Date Fair Value, Abstract
Weighted Average Grant Date Fair Value, Nonvested Beginning Balance \| $ / shares	$ 14.21
Weighted Average Grant Date Fair Value, Granted \| $ / shares	19.11
Weighted Average Grant Date Fair Value, Vested \| $ / shares	12.61
Weighted Average Grant Date Fair Value, Forfeited \| $ / shares	15.95
Weighted Average Grant Date Fair Value, Nonvested Ending Balance \| $ / shares	$ 17.28

Stock Options and Restricted Shares - Summary of Activity in Stock Options (Details) - $ / shares	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Shares, Abstract
Shares Outstanding, Beginning Balance	804,800
Shares Outstanding, Granted	0	0
Shares Outstanding, Exercised	(508,834)
Shares Outstanding, Ending Balance	295,966
Shares, Fully Vested and Expected to Vest	294,134
Shares, Exercisable at End of Period	268,466
Weighted Average Exercise Price, Abstract
Weighted Average Exercise Price Outstanding, Beginning Balance	$ 10.59
Weighted Average Exercise Price Outstanding, Exercised	10.11
Weighted Average Exercise Price Outstanding, Ending Balance	11.43
Weighted Average Exercise Price, Fully vested and expected to vest	11.42
Weighted Average Exercise Price, Exercisable at End of Period	$ 11.34
Weighted Average Remaining Contractual Term (year), Abstract
Weighted Average Remaining Contractual Term Outstanding	4 years
Weighted Average Remaining Contractual Term, Fully Vested and Expected to Vest	3 years 8 months 12 days
Weighted Average Remaining Contractual Term, Exercisable at End of Period	3 years 8 months 12 days

Stock Options and Restricted Shares - Information Related to Stock Options (Details) - USD ($)	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Intrinsic value of options exercised	$ 4,282,055	$ 684,275
Cash received from option exercises	5,144,090	821,500
Tax benefit realized from option exercises	$ 1,119,329	$ 263,446

Regulatory Capital Requirements - Schedule of Capital Amounts and Ratios (Details) - USD ($)
$ in Thousands

Sep. 30, 2018

Dec. 31, 2017

CapStar Financial Holdings, Inc.

Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]

Total capital to risk-weighted assets, actual amount

$ 171,866

$ 156,434

Tier I capital to risk-weighted assets, actual amount

156,469

142,534

Tier I capital to average assets, actual amount

$ 156,469

$ 142,534

Total capital to risk-weighted assets, actual ratio

12.62%

12.52%

Tier I capital to risk-weighted assets, actual ratio

11.49%

11.41%

Tier I capital to average assets, actual ratio

11.02%

10.77%

Total capital to risk-weighted assets, minimum capital requirement amount

^[1]

$ 108,958

$ 99,932

Tier I capital to risk-weighted assets, minimum capital requirement amount

^[1]

81,718

74,949

Tier I capital to average assets, minimum capital requirement amount

^[1]

$ 56,770

$ 53,218

Total capital to risk-weighted assets, minimum capital requirement ratio

^[1]

8.00%

Tier I capital to risk-weighted assets, minimum capital requirement ratio

^[1]

6.00%

Tier I capital to average assets, minimum capital requirement ratio

^[1]

4.00%

CapStar Financial Holdings, Inc. | Common Stock

Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]

Tier I capital to risk-weighted assets, actual amount

$ 147,469

$ 133,703

Tier I capital to risk-weighted assets, actual ratio

10.83%

10.70%

Tier I capital to risk-weighted assets, minimum capital requirement amount

^[1]

$ 61,289

$ 56,212

Tier I capital to risk-weighted assets, minimum capital requirement ratio

^[1]

4.50%

CapStar Bank

Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]

Total capital to risk-weighted assets, actual amount

$ 154,906

$ 142,396

Tier I capital to risk-weighted assets, actual amount

139,509

128,496

Tier I capital to average assets, actual amount

$ 139,509

$ 128,496

Total capital to risk-weighted assets, actual ratio

11.38%

11.40%

Tier I capital to risk-weighted assets, actual ratio

10.25%

10.29%

Tier I capital to average assets, actual ratio

9.83%

9.71%

Total capital to risk-weighted assets, minimum capital requirement amount

^[1]

$ 108,897

$ 99,928

Tier I capital to risk-weighted assets, minimum capital requirement amount

^[1]

81,673

74,946

Tier I capital to average assets, minimum capital requirement amount

^[1]

$ 56,760

$ 53,215

Total capital to risk-weighted assets, minimum capital requirement ratio

^[1]

8.00%

Tier I capital to risk-weighted assets, minimum capital requirement ratio

^[1]

6.00%

Tier I capital to average assets, minimum capital requirement ratio

^[1]

4.00%

Total capital to risk-weighted assets, minimum to be well capitalized amount

^[2]

$ 136,122

$ 124,909

Tier I capital to risk-weighted assets, minimum to be well capitalized amount

^[2]

108,897

99,928

Tier I capital to average assets, minimum to be well capitalized amount

^[2]

$ 70,950

$ 66,519

Total capital to risk-weighted assets, minimum to be well capitalized ratio

^[2]

10.00%

Tier I capital to risk-weighted assets, minimum to be well capitalized ratio

^[2]

8.00%

Tier I capital to average assets, minimum to be well capitalized ratio

^[2]

5.00%

CapStar Bank | Common Stock

Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]

Tier I capital to risk-weighted assets, actual amount

$ 123,009

$ 112,165

Tier I capital to risk-weighted assets, actual ratio

9.04%

8.98%

Tier I capital to risk-weighted assets, minimum capital requirement amount

^[1]

$ 61,255

$ 56,209

Tier I capital to risk-weighted assets, minimum capital requirement ratio

^[1]

4.50%

Tier I capital to risk-weighted assets, minimum to be well capitalized amount

^[2]

$ 88,479

$ 81,191

Tier I capital to risk-weighted assets, minimum to be well capitalized ratio

^[2]

6.50%

[1]	For the calendar year 2018, the Company must maintain a capital conservation buffer of Tier 1 common equity capital in excess of minimum risk-based capital ratios by at least 1.875% to avoid limits on capital distributions and certain discretionary bonus payments to executive officers and similar employees.
[2]	For the Company to be well-capitalized, the Bank must be well-capitalized and the Company must not be subject to any written agreement, order, capital directive, or prompt corrective action directive issued by the Federal Reserve to meet and maintain a specific capital level for any capital measure.

Earning Per Share - Summary of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Basic net income per share calculation:
Numerator – Net income	$ 3,656	$ 4,419	$ 10,363	$ 1,409
Denominator – Average common shares outstanding	12,040,229	11,279,364	11,851,476	11,239,093
Basic net income per share of common stock	$ 0.30	$ 0.39	$ 0.87	$ 0.13
Diluted net income per share calculation:
Numerator – Net income	$ 3,656	$ 4,419	$ 10,363	$ 1,409
Dilutive shares contingently issuable	1,073,546	1,471,059	1,201,282	1,518,998
Average diluted common shares outstanding	13,113,775	12,750,423	13,052,758	12,758,091
Diluted net income per share of common stock	$ 0.28	$ 0.35	$ 0.79	$ 0.11

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

+ References

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-Name Accounting Standards Codification
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Reference 3: http://www.xbrl.org/2003/role/exampleRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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-SubTopic 10
-Section 45
-Paragraph 60B
-Subparagraph (d)
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+ Details

- Definition

The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=109256448&loc=d3e4984-109258

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+ Details

Fair Value - Additional Information (Details) - USD ($)	Sep. 30, 2018	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Other real estate owned	$ 0	$ 0
Loans held for sale carried at fair value	$ 0	$ 0

Fair Value - Summary of Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Assets:
Total securities available for sale	$ 187,469	$ 192,621
Obligations of States and Political Subdivisions
Assets:
Total securities available for sale	44,245	52,998
Asset-backed securities
Assets:
Total securities available for sale	15,713	16,377
Other debt securities
Assets:
Total securities available for sale	11,844	5,407
Fair Value Measurements Recurring Basis
Assets:
Total securities available for sale	187,469	192,621
Liabilities:
Total derivatives	(1,086)	(1,559)
Fair Value Measurements Recurring Basis \| U.S. Government-sponsored Agencies
Assets:
Total securities available for sale	10,465	11,277
Fair Value Measurements Recurring Basis \| Obligations of States and Political Subdivisions
Assets:
Total securities available for sale	44,245	52,998
Fair Value Measurements Recurring Basis \| Mortgage-backed Securities-residential
Assets:
Total securities available for sale	105,202	106,562
Fair Value Measurements Recurring Basis \| Asset-backed securities
Assets:
Total securities available for sale	15,713	16,377
Fair Value Measurements Recurring Basis \| Other debt securities
Assets:
Total securities available for sale	11,844	5,407
Fair Value Measurements Recurring Basis \| Interest Rate Swaps - Customer Related
Assets:
Interest rate swaps - customer related	624	184
Liabilities:
Total Derivatives:	(624)	(184)
Fair Value Measurements Recurring Basis \| Interest Rate Swaps - Cash Flow Hedges
Liabilities:
Total Derivatives:	(462)	(1,375)
Fair Value Measurements Recurring Basis \| Significant Other Observable Inputs (Level 2)
Assets:
Total securities available for sale	187,469	192,621
Liabilities:
Total derivatives	(1,086)	(1,559)
Fair Value Measurements Recurring Basis \| Significant Other Observable Inputs (Level 2) \| U.S. Government-sponsored Agencies
Assets:
Total securities available for sale	10,465	11,277
Fair Value Measurements Recurring Basis \| Significant Other Observable Inputs (Level 2) \| Obligations of States and Political Subdivisions
Assets:
Total securities available for sale	44,245	52,998
Fair Value Measurements Recurring Basis \| Significant Other Observable Inputs (Level 2) \| Mortgage-backed Securities-residential
Assets:
Total securities available for sale	105,202	106,562
Fair Value Measurements Recurring Basis \| Significant Other Observable Inputs (Level 2) \| Asset-backed securities
Assets:
Total securities available for sale	15,713	16,377
Fair Value Measurements Recurring Basis \| Significant Other Observable Inputs (Level 2) \| Other debt securities
Assets:
Total securities available for sale	11,844	5,407
Fair Value Measurements Recurring Basis \| Significant Other Observable Inputs (Level 2) \| Interest Rate Swaps - Customer Related
Assets:
Interest rate swaps - customer related	624	184
Liabilities:
Total Derivatives:	(624)	(184)
Fair Value Measurements Recurring Basis \| Significant Other Observable Inputs (Level 2) \| Interest Rate Swaps - Cash Flow Hedges
Liabilities:
Total Derivatives:	$ (462)	$ (1,375)

Fair Value - Summary of Quantitative Information About Level 3 Fair Value Measurements for Assets Measured at Fair Value on a Non-Recurring Basis (Details) - Fair Value, Measurements, Nonrecurring [Member] $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Commercial and industrial
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impaired loans	$ 2,719	$ 1,388
Significant Unobservable Inputs (Level 3)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Unobservable Input(s)	Loss severity
Significant Unobservable Inputs (Level 3) \| Measurement Input, Discount Rate \| Minimum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Valuation Technique(s)	5%
Significant Unobservable Inputs (Level 3) \| Measurement Input, Discount Rate \| Maximum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Valuation Technique(s)	50%
Significant Unobservable Inputs (Level 3) \| Commercial and industrial
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Impaired loans	$ 2,719	$ 1,388
Valuation Technique(s)	Discounted cash flow	Dec. 31, 2017: Sales comparison approach
Unobservable Input(s)	Probability of default	Dec. 31, 2017:Appraisal discounts
Range (Weighted-Average)		0.15
Significant Unobservable Inputs (Level 3) \| Commercial and industrial \| Measurement Input, Discount Rate \| Minimum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Valuation Technique(s)	5%
Significant Unobservable Inputs (Level 3) \| Commercial and industrial \| Measurement Input, Discount Rate \| Maximum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Valuation Technique(s)	60%

Fair Value - Summary of Carrying Value and Fair Values of the Bank's Financial Instruments (Details) - USD ($)	Sep. 30, 2018	Dec. 31, 2017
Financial assets:
Securities available-for-sale	$ 187,469,000	$ 192,621,000
Securities held to maturity, fair value	3,766,000	3,848,000
Loans held for sale	0	0
Carrying amount
Financial assets:
Restricted equity securities	8,817,000	8,806,000
Carrying amount \| Level 1
Financial assets:
Cash and due from banks, interest-bearing deposits in financial institutions	49,842,000	78,078,000
Federal funds sold	2,747,000	4,719,000
Carrying amount \| Level 2
Financial assets:
Securities available-for-sale	187,469,000	192,621,000
Securities held to maturity, fair value	3,740,000	3,759,000
Loans held for sale	50,499,000	74,093,000
Accrued interest receivable	4,430,000	4,084,000
Other assets	23,519,000	22,663,000
Financial liabilities:
Federal Home Loan Bank advances	125,000,000	70,000,000
Carrying amount \| Significant Unobservable Inputs (Level 3)
Financial assets:
Loans, net	1,073,870,000	947,537,000
Financial liabilities:
Deposits	1,126,403,000	1,119,866,000
Other liabilities	2,447,000	3,672,000
Fair value \| Level 1
Financial assets:
Cash and due from banks, interest-bearing deposits in financial institutions	49,842,000	78,078,000
Federal funds sold	2,747,000	4,719,000
Fair value \| Level 2
Financial assets:
Securities available-for-sale	187,469,000	192,621,000
Securities held to maturity, fair value	3,766,000	3,848,000
Loans held for sale	51,326,000	75,549,000
Accrued interest receivable	4,430,000	4,084,000
Other assets	23,519,000	22,663,000
Financial liabilities:
Federal Home Loan Bank advances	124,983,000	69,980,000
Fair value \| Significant Unobservable Inputs (Level 3)
Financial assets:
Loans, net	1,065,226,000	944,037,000
Financial liabilities:
Deposits	1,074,725,000	1,065,669,000
Other liabilities	$ 2,447,000	$ 3,672,000

Subsequent Events - Additional Information (Details) - Subsequent Event	Oct. 01, 2018 USD ($) $ / shares shares
Subsequent Event [Line Items]
Purchase price consideration \| $	$ 92,900,000
Athens Bancshares Corporation
Subsequent Event [Line Items]
Common stock, par value \| $ / shares	$ 0.01
CapStar Financial Holdings, Inc.
Subsequent Event [Line Items]
Conversion of debt exchange ratio	2.864
Common stock, shares issued \| shares	5,181,916
converted options right to purchase shares of CapStar Common Stock, shares \| shares	548,051
converted options right to purchase shares of CapStar Common Stock, per share \| $ / shares	$ 5.06

Regulatory Capital Requirements - Schedule of Capital Amounts and Ratios (Parenthetical) (Details)	Sep. 30, 2018
Banking And Thrift [Abstract]
Minimum risk based capital ratios	1.875%