Borrowed Funds - Schedule of Long-Term Borrowings (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Total long-term borrowings	$ 1,654,268	$ 2,315,819
Long-term borrowings
Debt Instrument [Line Items]
FHLB advances, net	1,309,666	1,980,666
Subordinated debt, net	294,602	235,153
Securities sold under agreements to repurchase	50,000	100,000
Total long-term borrowings	1,654,268	2,315,819
Unamortized prepayment penalties and other purchase accounting adjustments	10,300	14,300
Deferred issuance costs	$ 1,400	$ 1,700