Loans - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-PCI loans net of premiums and deferred loan fees	$ 12,600,000	$ 21,500,000
Loans	29,699,208,000	25,035,469,000
Loans transferred to loans held for sale	1,234,022,000	289,633,000	$ 313,201,000
Sales of loans	0	0
Net increase (decrease) in expected cash flows	$ (11,000,000.0)	269,800,000
Combined loan-to-value ratio home equity loan	80.00%
Accrued interest on non-accrual loans	$ 2,500,000	3,600,000	$ 2,500,000
Number of consecutive months for performing restructured loans to be put on accrual status	6 months
TDRs not reported as non-accrual loans	$ 73,000,000.0	77,200,000
Non-performing TDRs	65,100,000	55,000,000.0
Specific reserves for loan losses	36,000,000.0	6,500,000
Troubled debt restructuring, charge-offs	$ 4,900,000	$ 0
Number of days loans placed on non-accrual status	90 days	90 days
PCI Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 6,629,599,000	$ 4,190,086,000
PCI Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	6,800,000,000	4,400,000,000
Commitments under unused lines of credit—credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unsecured loans	8,200,000	10,400,000
Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	4,377,111,000	4,111,400,000
Loans transferred to loans held for sale	436,500,000	289,600,000
Residential mortgage | PCI Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	580,169,000	428,416,000
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	17,643,759,000	13,895,407,000
Loans transferred to loans held for sale	798,000,000
Commercial real estate | PCI Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	5,245,149,000	2,860,750,000
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	4,825,997,000	4,331,032,000
Unsecured loans	606,100,000	580,500,000
Impaired loans	250,000
Commercial and industrial | PCI Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	682,014,000	740,657,000
Commercial and industrial | Tax Medallion
Accounts, Notes, Loans and Financing Receivable [Line Items]
Taxi medallion loans	114,800,000
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,852,341,000	2,697,630,000
Unsecured loans	53,900,000	58,100,000
Consumer | PCI Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 122,267,000	$ 160,263,000