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	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Change in fair value:
Changes in valuation included in other noninterest income	$ 4,898
Carrying amount
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Carrying value at beginning of period	239,063	$ 0
Commercial loans held for sale acquired from Franklin		350,269
Change in fair value:
Pay-downs and pay-offs	(141,002)	(111,206)
Write-offs to discount	(8,563)	0
Changes in valuation included in other noninterest income	(2,736)	0
Carrying value at end of period	86,762	239,063
Fair Value Discount
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Carrying value at beginning of period	(23,660)	0
Commercial loans held for sale acquired from Franklin		(24,063)
Change in fair value:
Pay-downs and pay-offs	0	0
Write-offs to discount	8,563	(2,825)
Changes in valuation included in other noninterest income	7,634	3,228
Carrying value at end of period	(7,463)	(23,660)
Fair Value
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Carrying value at beginning of period	215,403	0
Commercial loans held for sale acquired from Franklin		326,206
Change in fair value:
Pay-downs and pay-offs	(141,002)	(111,206)
Write-offs to discount	0	(2,825)
Changes in valuation included in other noninterest income		3,228
Carrying value at end of period	$ 79,299	$ 215,403