Loans and Allowance for Credit Losses for Loans - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non covered loans net of unearned discount and deferred loan fees	$ 110,900,000		$ 110,900,000		$ 120,500,000
Accrued interest	214,500,000		214,500,000		175,900,000
Transfer of loans to loans held for sale			10,000,000	$ 0
Allowance for credit loss, write-off			4,200,000
Sales of loans	0	$ 0	0	0
Specific reserves for loan losses		71,500,000		71,500,000
Loan charge-offs related to loans modified as TDRs		3,800,000		5,400,000
TDRs not reported as non-accrual loans		69,700,000		69,700,000
Non-performing TDRs		$ 155,700,000		$ 155,700,000
Other real estate owned	0		0		0
Allowance for purchase credit deteriorated (PCD) loans			20,900,000
Residential real estate properties
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other real estate owned	0		0		0
In formal foreclosure proceedings
Accounts, Notes, Loans and Financing Receivable [Line Items]
Residential mortgage and consumer loans secured by residential real estate properties	$ 970,000		$ 970,000		$ 2,600,000