Borrowed Funds - Schedule of Long-Term Borrowings (Details) - Long-term borrowings - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
FHLB advances, net	$ 1,592,252	$ 1,480,012
Subordinated debt, net	403,413	292,414
Securities sold under agreements to repurchase	300,000	350,000
Total long-term borrowings	2,295,665	2,122,426
Unamortized prepayment penalties and other purchase accounting adjustments	2,600	2,800
Deferred issuance costs	$ 2,700	$ 1,200