Borrowed Funds - Schedule of Long-Term Borrowings (Detail) - Long-term borrowings - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
FHLB advances, net	$ 1,480,012	$ 1,309,666
Securities sold under agreements to repurchase	350,000	50,000
Subordinated debt, net	292,414	294,602
Total long-term borrowings	2,122,426	1,654,268
Unamortized prepayment penalties and other purchase accounting adjustments	2,800	10,300
Deferred issuance costs	$ 1,200	$ 1,400