Fair Value of Financial Instruments - Schedule of Changes in Fair Value Associated with Commercial Loans Held for Sale (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2023
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	Changes in valuation included in other noninterest income
Franklin Financial Network, Inc. | Commercial and industrial | Principal balance
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Carrying value at beginning of period	$ 12,232	$ 34,357
Change in fair value:
Paydowns and payoffs		(22,125)
Changes in valuation included in other noninterest income	0	0
Carrying value at end of period	12,232	12,232
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	(2,965)	(3,867)
Change in fair value:
Paydowns and payoffs		0
Changes in valuation included in other noninterest income	(7)	895
Carrying value at end of period	(2,972)	(2,972)
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	9,267	30,490
Change in fair value:
Paydowns and payoffs		(22,125)
Changes in valuation included in other noninterest income	(7)	895
Carrying value at end of period	$ 9,260	$ 9,260