| Document and Entity Information | Jul. 01, 2020 |
| Cover [Abstract] | |
| Entity Incorporation, State or Country Code | TN |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, $1.00 par value per share |
| Security Exchange Name | NASDAQ |
| Amendment Description | On July 1, 2020, CapStar Financial Holdings, Inc., a Tennessee corporation (“CapStar”), filed with the U.S. Securities and Exchange Commission (the “SEC”) a Current Report on Form 8-K (the “Initial 8-K”) to disclose that it had completed its previously announced acquisitions of FCB Corporation, a Tennessee corporation (“FCB”) and The Bank of Waynesboro, a Tennessee chartered bank (“BOW”). This Form 8-K/A amends the Initial 8-K to include the historical audited and unaudited financial statements of FCB and BOW and the pro forma combined financial information required by Items 9.01(a) and 9.01(b) of Form 8-K that were excluded from the Initial 8-K in reliance on the instructions to such items. |
| Document Type | 8-K/A |
| Amendment Flag | true |
| Document Period End Date | Jul. 1, 2020 |
| Trading Symbol | CSTR |
| Entity Registrant Name | CAPSTAR FINANCIAL HOLDINGS, INC. |
| Entity Central Index Key | 0001676479 |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | true |
| Entity File Number | 001-37886 |
| Entity Tax Identification Number | 81-1527911 |
| Entity Address, Address Line One | 1201 Demonbreun Street |
| Entity Address, Address Line Two | Suite 700 |
| Entity Address, City or Town | Nashville |
| Entity Address, State or Province | TN |
| Entity Address, Postal Zip Code | 37203 |
| City Area Code | 615 |
| Local Phone Number | 732-6400 |
