Summary of Significant Accounting Policies (Policies)	6 Months Ended
Jun. 30, 2022
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited consolidated financial statements as of and for the period ended June 30, 2022 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 notes 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 2021 Form 10-K.
Business Combinations	Business Combinations The Company accounts for business combinations using the acquisition method of accounting. The accounts of an acquired entity are included as of the date of acquisition, and any excess of purchase price over the fair value of the net assets acquired is capitalized as goodwill. Under this method, all identifiable assets acquired, including purchased loans, and liabilities assumed are recorded at fair value. The Company typically issues common stock and/or pays cash for an acquisition, depending on the terms of the acquisition agreement. The value of shares of common stock issued is determined based upon the market price of the stock as of the closing of the acquisition.
Reclassifications	Reclassifications Certain amounts, previously reported, have been reclassified to state all periods on a comparable basis and had no effect on shareholders' equity or net income.
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, the valuation of loans held for sale, deferred tax assets and estimated liabilities. There have been no significant changes to the Company’s critical accounting policies and estimates as disclosed in the 2021 Form 10-K.
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. On July 28, 2022, the Company entered into a letter of intent to sell $64.8 million in Tri-Net loans held for sale. Those loans will be sold at a loss of approximately $1.2 million after tax. Included within this sale was $53.7 million classified as loans held for sale as of June 30, 2022. The Company expects to finalize this sale during the third quarter of 2022. The Company evaluated all other significant events or transactions that occurred after June 30, 2022 through the date of filing this Quarterly Report on Form 10-Q and determined that there were no other events that required disclosure.

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Disclosure of accounting policy for basis of accounting, or basis of presentation, used to prepare the financial statements (for example, US Generally Accepted Accounting Principles, Other Comprehensive Basis of Accounting, IFRS).

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Disclosure of accounting policy for completed business combinations (purchase method, acquisition method or combination of entities under common control). This accounting policy may include a general discussion of the purchase method or acquisition method of accounting (including for example, the treatment accorded contingent consideration, the identification of assets and liabilities, the purchase price allocation process, how the fair values of acquired assets and liabilities are determined) and the entity's specific application thereof. An entity that acquires another entity in a leveraged buyout transaction generally discloses the accounting policy followed by the acquiring entity in determining the basis used to value its interest in the acquired entity, and the rationale for that accounting policy.

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Disclosure of accounting policy for reclassification affecting comparability of financial statement. Excludes amendment to accounting standards, other change in accounting principle, and correction of error.

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