Loans and Allowance for Credit Losses for Loans - Additional Information (Details)	3 Months Ended
	Mar. 31, 2020 USD ($) component SecurityLoan	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans net of unearned premiums and deferred loan fees	$ 76,400,000		$ 12,600,000
Accrued interest	87,300,000		86,300,000
Transfer of loans to loans held for sale	30,020,000	$ 99,976,000
Sales of loans	$ 0	0
Days past due to place on non-accrual status	90 days
Number of consecutive months for performing restructured loans to be put on accrual status	6 months
TDRs not reported as non-accrual loans	$ 48,000,000.0		73,000,000.0
Non-performing TDRs	89,100,000		65,100,000
Specific reserves for loan losses	7,900,000	7,900,000
Loan charge-offs related to loans modified as TDRs	$ 791,000	913,000
Number of modified loans | SecurityLoan	2,100
Other real estate owned	$ 10,200,000		9,400,000
Number of basic components | component	2
Forecast period	2 years
Historical loss experience period	1 year
Allowance for unfunded credit commitments	$ 10,019,000		2,845,000
Allowance for PCD loans reclassification	61,600,000
Residential real estate properties
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other real estate owned	2,600,000		2,100,000
In formal foreclosure proceedings
Accounts, Notes, Loans and Financing Receivable [Line Items]
Residential mortgage and consumer loans secured by residential real estate properties	1,800,000		$ 2,800,000
Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Transfer of loans to loans held for sale	$ 30,000,000.0	$ 100,000,000.0