Stock Options and Restricted Shares - Additional Information (Details) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2022	Jun. 30, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options granted	0	0
Performance Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period	3 years
Restricted Shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total unrecognized compensation cost	$ 2.2
Cost expected to be recognized over a weighted-average period	2 years 1 month 6 days
Total fair value of shares vested	$ 0.6
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period	3 years
Contractual term	10 years
Minimum \| Time-Vested Restricted Stock Units and Performance Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period	2 years
Minimum \| Performance Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Awards earning percentage	0.00%
Maximum \| Time-Vested Restricted Stock Units and Performance Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period	3 years
Maximum \| Performance Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Awards earning percentage	188.00%
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	1,168,543
Shares issuable under both restricted share and stock option grants	1,102,218

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Aggregate number of common shares reserved for future issuance.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Amount of cost to be recognized for nonvested award under share-based payment arrangement. Excludes share and unit options.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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Gross number of share options (or share units) granted during the period.

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