Noninterest Income - Lending Related Fees (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Lending related fees	$ 10,675	$ 15,404	$ 30,938	$ 32,874
Unused commitment fees
Accounts, Notes, Loans and Financing Receivable [Line Items]
Lending related fees	8,410	12,334	24,994	25,923
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Lending related fees	$ 2,265	$ 3,070	$ 5,944	$ 6,951