Borrowed Funds - Schedule of Long-Term Borrowings (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Net subordinated note carrying value	$ 113,100
Long-term borrowings
Debt Instrument [Line Items]
FHLB advances, net	2,153,052	$ 1,480,012
Net subordinated note carrying value	404,455	292,414
Securities sold under agreements to repurchase	350,000	350,000
Other	28	0
Total long-term borrowings	2,907,535	2,122,426
Unamortized prepayment penalties and other purchase accounting adjustments	1,200	2,800
Deferred issuance costs	$ 2,900	$ 1,200