Borrowed Funds - Additional Information (Details) - USD ($)			1 Months Ended				12 Months Ended
	Jun. 05, 2020	Jan. 01, 2018	Sep. 30, 2020	Aug. 31, 2016	Jun. 30, 2015	Sep. 30, 2013	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Weighted average interest rate for short-term borrowings							0.38%	1.68%
FHLB advances callable for early redemption							$ 0
Prepaid long-term FHLB advances							$ 534,300,000	$ 635,000,000.0
Callable FHLB advances interest rate							2.48%	3.93%
Loss on extinguishment of debt							$ 12,036,000	$ 31,995,000	$ 0
Subordinated notes, interest rate	5.25%
Net carrying value of subordinated debentures							113,300,000
Fair value of securities							2,100,000,000	$ 2,300,000,000
FHLB
Debt Instrument [Line Items]
Amount of hedged debt							$ 200,000,000
Interest rate swaps
Debt Instrument [Line Items]
Notional amount of terminated derivative				$ 125,000,000
Securities sold under agreements to repurchase
Debt Instrument [Line Items]
Weighted average interest rate for long-term borrowings							3.37%	1.94%
Subordinated Debt
Debt Instrument [Line Items]
Face value	$ 115,000,000
Subordinated debt initial term	5 years
Subordinated debt SOFR term	3 months
Subordinated Debt | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Debt Instrument [Line Items]
Subordinated debt basis points	5.14%
FHLB
Debt Instrument [Line Items]
Amount of hedged debt							$ 900,000,000
Loss on extinguishment of debt							$ 9,700,000
FHLB
Debt Instrument [Line Items]
Weighted average interest rate for long-term borrowings							2.02%	2.23%
Subordinated notes
Debt Instrument [Line Items]
Subordinated notes, interest rate					4.55%
Net carrying value of subordinated debentures							$ 99,500,000	$ 99,400,000
Subordinated notes					$ 100,000,000
Subordinated notes due September 2023
Debt Instrument [Line Items]
Subordinated notes, interest rate						5.125%
Net carrying value of subordinated debentures							130,500,000	132,400,000
Subordinated notes						$ 125,000,000
Effective interest rate				3.32%
Subordinated Notes Due January 2022
Debt Instrument [Line Items]
Loss on extinguishment of debt							2,400,000
Prepayment of long-term borrowings			$ 50,000,000
Long-term borrowing interest rate			3.70%
USAmeriBancorp, Inc.
Debt Instrument [Line Items]
Subordinated notes, interest rate		6.25%
Net carrying value of subordinated debentures							$ 60,100,000	$ 60,600,000
Subordinated notes		$ 60,000,000