Fair Value of Financial Instruments - Changes in Fair Value Associated with Commercial Loans Held for Sale (Details) - Franklin Financial Network, Inc. - Commercial and industrial - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Aggregate Unpaid Principal Balance
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Carrying value at beginning of period	$ 86,762	$ 239,063
Change in fair value:
Pay-downs and pay-offs	(946)	(39,566)
Write-offs to discount	0	(2,007)
Changes in valuation included in other noninterest income	0	0
Carrying value at end of period	85,816	197,490
Fair Value Discount
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Carrying value at beginning of period	(7,463)	(23,660)
Change in fair value:
Pay-downs and pay-offs	0	0
Write-offs to discount	0	2,007
Changes in valuation included in other noninterest income	(174)	(853)
Carrying value at end of period	(7,637)	(22,506)
Fair Value
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Carrying value at beginning of period	79,299	215,403
Change in fair value:
Pay-downs and pay-offs	(946)	(39,566)
Write-offs to discount	0	0
Changes in valuation included in other noninterest income	(174)	(853)
Carrying value at end of period	$ 78,179	$ 174,984