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