Regulatory Capital Requirements - Schedule of Capital Amounts and Ratios (Details) $ in Thousands		Jun. 30, 2022 USD ($)	Dec. 31, 2021 USD ($)
CapStar Financial Holdings, Inc.
Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]
Total capital to risk-weighted assets, actual amount		$ 396,660	$ 384,116
Tier I capital to risk-weighted assets, actual amount		345,058	332,567
Tier I capital to average assets, actual amount		$ 345,058	$ 332,567
Total capital to risk-weighted assets, actual ratio		14.79	16.29
Tier I capital to risk-weighted assets, actual ratio		12.87	14.11
Tier I capital to average assets, actual ratio		11.10	10.69
Total capital to risk-weighted assets, minimum capital requirement amount	[1]	$ 214,487	$ 188,610
Tier I capital to risk-weighted assets, minimum capital requirement amount	[1]	160,865	141,458
Tier I capital to average assets, minimum capital requirement amount	[1]	$ 124,395	$ 124,437
Total capital to risk-weighted assets, minimum capital requirement ratio	[1]	8.0	8.0
Tier I capital to risk-weighted assets, minimum capital requirement ratio	[1]	6.0	6.0
Tier I capital to average assets, minimum capital requirement ratio	[1]	4.0	4.0
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		$ 345,058	$ 332,567
Tier I capital to risk-weighted assets, actual ratio		12.87	14.11
Tier I capital to risk-weighted assets, minimum capital requirement amount	[1]	$ 120,649	$ 106,093
Tier I capital to risk-weighted assets, minimum capital requirement ratio	[1]	4.5	4.5
CapStar Bank
Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]
Total capital to risk-weighted assets, actual amount		$ 384,194	$ 370,919
Tier I capital to risk-weighted assets, actual amount		362,191	348,902
Tier I capital to average assets, actual amount		$ 362,191	$ 348,902
Total capital to risk-weighted assets, actual ratio		14.34	15.74
Tier I capital to risk-weighted assets, actual ratio		13.52	14.81
Tier I capital to average assets, actual ratio		11.66	11.23
Total capital to risk-weighted assets, minimum capital requirement amount	[1]	$ 214,387	$ 188,471
Tier I capital to risk-weighted assets, minimum capital requirement amount	[1]	160,790	141,354
Tier I capital to average assets, minimum capital requirement amount	[1]	$ 124,276	$ 124,246
Total capital to risk-weighted assets, minimum capital requirement ratio	[1]	8.0	8.0
Tier I capital to risk-weighted assets, minimum capital requirement ratio	[1]	6.0	6.0
Tier I capital to average assets, minimum capital requirement ratio	[1]	4.0	4.0
Total capital to risk-weighted assets, minimum to be well capitalized amount	[2]	$ 267,983	$ 235,589
Tier I capital to risk-weighted assets, minimum to be well capitalized amount	[2]	214,387	188,471
Tier I capital to average assets, minimum to be well capitalized amount	[2]	$ 155,345	$ 155,308
Total capital to risk-weighted assets, minimum to be well capitalized ratio	[2]	10	10.0
Tier I capital to risk-weighted assets, minimum to be well capitalized ratio	[2]	8.00	8.0
Tier I capital to average assets, minimum to be well capitalized ratio	[2]	5.00	5.0
CapStar Bank | Common Stock
Compliance With Regulatory Capital Requirements Under Banking Regulations [Line Items]
Tier I capital to risk-weighted assets, actual amount		$ 345,691	$ 332,402
Tier I capital to risk-weighted assets, actual ratio		12.90	14.11
Tier I capital to risk-weighted assets, minimum capital requirement amount	[1]	$ 120,592	$ 106,015
Tier I capital to risk-weighted assets, minimum capital requirement ratio	[1]	4.5	4.5
Tier I capital to risk-weighted assets, minimum to be well capitalized amount	[2]	$ 174,189	$ 153,133
Tier I capital to risk-weighted assets, minimum to be well capitalized ratio	[2]	6.50	6.5

[1] For the calendar year 2022, 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 2.5% 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.