Loans and Allowance for Credit Losses for Loans - Additional Information (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($) component	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) component SecurityLoan	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-covered loans net of unearned premiums and deferred loan fees	$ 131,300,000		$ 131,300,000		$ 12,600,000
Accrued interest	104,200,000		104,200,000		86,300,000
Transfer of loans to loans held for sale			30,020,000	$ 216,301,000
Sales of loans			$ 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	53,900,000		$ 53,900,000		73,000,000.0
Non-performing TDRs	85,600,000		85,600,000		65,100,000
Specific reserves for loan losses			8,400,000	11,700,000
Loan charge-offs related to loans modified as TDRs	2,900,000	$ 1,100,000	$ 3,700,000	2,000,000.0
Number of modified loans | SecurityLoan			7,000
Amount from modified loans			$ 3,100,000,000
Other real estate owned	$ 8,300,000		$ 8,300,000		9,400,000
Number of basic components | component	2		2
Forecast period			2 years
Historical loss experience period			1 year
Allowance for unfunded credit commitments	$ 10,109,000		$ 10,109,000		2,845,000
Residential real estate properties
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other real estate owned	2,500,000		2,500,000		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		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	$ 216,300,000
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired loans threshold					$ 250,000