Borrowed Funds - Schedule of Long-Term Borrowings (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Apr. 01, 2021	Dec. 31, 2020
Long-term borrowings
Debt Instrument [Line Items]
FHLB advances, net	$ 947,206		$ 1,592,252
Subordinated debt, net	638,484		403,413
Securities sold under agreements to repurchase	300,000		300,000
Total long-term borrowings	1,885,690		2,295,665
Unamortized prepayment penalties and other purchase accounting adjustments			2,600
Deferred issuance costs	6,400,000		$ 2,700
Subordinated Notes Due June 2030
Debt Instrument [Line Items]
Subordinated debt, net	115,000
Subordinated Notes Due June 2025
Debt Instrument [Line Items]
Subordinated debt, net	100,000
Subordinated Notes Due September 2023
Debt Instrument [Line Items]
Subordinated debt, net	$ 125,000
Subordinated Notes Due April 2026
Debt Instrument [Line Items]
Subordinated debt, net		$ 60,000