Loans and Allowance for Credit Losses for Loans - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-PCI loans net of premiums and deferred loan fees	$ 95,800,000	$ 12,600,000
Accrued interest	90,200,000	86,300,000
Loans transferred to loans held for sale	30,020,000	1,234,022,000	$ 289,633,000
Sales of loans	0	0
Net loans	31,876,869,000	29,537,449,000
Allowance for loan losses	$ 340,243,000	161,759,000	151,859,000
Combined loan-to-value ratio home equity loan	80.00%
Accrued interest on non-accrual loans	$ 6,200,000	2,500,000	3,600,000
Number of consecutive months for performing restructured loans to be put on accrual status	6 months
TDRs not reported as non-accrual loans	$ 57,400,000	73,000,000.0
Non-performing TDRs	92,800,000	65,100,000
Specific reserves for loan losses	21,100,000	36,000,000.0
Troubled debt restructuring, charge-offs	7,700,000	4,900,000
Amount from modified loans	361,000,000
Net decrease in expected cash flows	(10,995,000)	(11,000,000.0)
Commitments under unused lines of credit—credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unsecured loans	8,800,000	8,200,000
Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans transferred to loans held for sale	30,000,000.0	436,500,000
Allowance for loan losses	28,873,000	5,060,000	5,041,000
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans transferred to loans held for sale		798,000,000
Unsecured loans	2,700,000,000	606,100,000
Allowance for loan losses	131,070,000	104,059,000	90,956,000
Impaired loans		250,000
Commercial and industrial | Tax Medallion
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net loans	97,500,000
Allowance for loan losses	66,400,000
Commercial and industrial | SBA guaranteed PPP loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unsecured loans	2,200,000,000
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unsecured loans	49,400,000	53,900,000
Allowance for loan losses	$ 16,187,000	$ 6,967,000	$ 6,212,000