Loans - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non-PCI loans net of premiums and deferred loan fees	$ 21,500,000	$ 22,200,000
Loans	25,035,469,000	18,331,580,000
Loans transferred to loans held for sale	289,633,000	313,201,000	$ 174,501,000
Sales of loans	0	0
Net increase in expected cash flows	$ 269,800,000	77,300,000
Combined loan-to-value ratio home equity loan	80.00%
Accrued interest on non-accrual loans	$ 3,600,000	2,500,000	$ 2,100,000
Number of consecutive months for performing restructured loans to be put on accrual status	6 months
TDRs not reported as non-accrual loans	$ 77,200,000	117,200,000
Non-performing TDRs	55,000,000	27,000,000
Specific reserves for loan losses	6,500,000	8,700,000
Troubled debt restructuring, charge-offs	$ 0	$ 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	$ 4,190,086,000	$ 1,387,215,000
PCI Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	4,400,000,000	1,500,000,000
Commitments under unused lines of credit—credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unsecured loans	10,400,000	8,200,000
Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	4,111,400,000	2,859,035,000
Loans transferred to loans held for sale	289,600,000	313,200,000
Residential mortgage | PCI Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	428,416,000	141,291,000
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	4,331,032,000	2,741,425,000
Unsecured loans	580,500,000	401,800,000
Impaired loans	250,000
Commercial and industrial | PCI Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	740,657,000	192,360,000
Commercial and industrial | Tax Medallion
Accounts, Notes, Loans and Financing Receivable [Line Items]
Taxi medallion loans	130,200,000
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,697,630,000	2,383,238,000
Unsecured loans	58,100,000	18,100,000
Consumer | PCI Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 160,263,000	$ 77,497,000