Fair Value of Financial Instruments - Schedule of Changes in Fair Value Associated with Commercial Loans Held for Sale (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Change in fair value:
Fair Value Recurring Basis Unobservable Input Reconciliation Asset Gain Loss Statement Of Income Extensible List Not Disclosed Flag	Changes in valuation included in other noninterest income
Franklin Financial Network, Inc. | Commercial and industrial | Aggregate Unpaid Principal Balance
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Carrying value at beginning of period	$ 34,357	$ 86,762	$ 239,063
Change in fair value:
Pay-downs and pay-offs	(28,376)	(43,676)	(141,002)
Write-offs to discount	(5,981)	(8,729)	(8,563)
Changes in valuation included in other noninterest income	0	0	(2,736)
Carrying value at end of period	0	34,357	86,762
Franklin Financial Network, Inc. | Commercial and industrial | Fair Value Discount
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Carrying value at beginning of period	(3,867)	(7,463)	(23,660)
Change in fair value:
Pay-downs and pay-offs	0	0	0
Write-offs to discount	5,981	8,729	8,563
Changes in valuation included in other noninterest income	(2,114)	(5,133)	7,634
Carrying value at end of period	0	(3,867)	(7,463)
Franklin Financial Network, Inc. | Commercial and industrial |  Fair Value
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Carrying value at beginning of period	30,490	79,299	215,403
Change in fair value:
Pay-downs and pay-offs	(28,376)	(43,676)	(141,002)
Write-offs to discount	0	0	0
Changes in valuation included in other noninterest income	(2,114)	(5,133)	4,898
Carrying value at end of period	$ 0	$ 30,490	$ 79,299