Loans and Allowance for Credit Losses for Loans - Additional Information (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non covered loans net of unearned discount and deferred loan fees	$ 86,100,000		$ 86,100,000		$ 95,800,000
Accrued interest	84,100,000		84,100,000		90,200,000
Transfer of loans to loans held for sale			0	$ 30,020,000
Sales of loans	0	$ 0	$ 0	0
Number of consecutive months for performing restructured loans to be put on accrual status			6 months
TDRs not reported as non-accrual loans	64,100,000		$ 64,100,000		57,400,000
Non-performing TDRs	89,800,000		89,800,000		92,800,000
Specific reserves for loan losses	4,500,000	8,400,000	4,500,000	8,400,000
Loan charge-offs related to loans modified as TDRs	697,000	$ 2,900,000	5,800,000	3,700,000
Amount from modified loans	142,000,000		142,000,000		361,000,000
Other real estate owned	4,500,000		4,500,000		5,100,000
Residential real estate properties
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other real estate owned	0		0		1,000,000.0
In formal foreclosure proceedings
Accounts, Notes, Loans and Financing Receivable [Line Items]
Residential mortgage and consumer loans secured by residential real estate properties	$ 2,000,000.0		$ 2,000,000.0		$ 1,900,000
Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Transfer of loans to loans held for sale				$ 30,000,000.0