Investment Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Contractual maturities of investments in debt securities available-for-sale, Amortized Cost
Due in one year or less	$ 96,850
Due after one year through five years	586,850
Due after five years through ten years	112,742
Due after ten years	470
Mortgage-backed securities	484,888
Total debt securities available-for-sale	1,281,800	$ 1,173,268
Contractual maturities of investments in debt securities available-for-sale, Fair Value
Due in one year or less	97,884
Due after one year through five years	592,948
Due after five years through ten years	110,586
Due after ten years	432
Mortgage-backed securities	489,490
Total debt securities available-for-sale	1,291,340	1,197,467
Accrued interest receivable on investment securities available-for-sale	3,980	3,840
U.S. Treasury and Federal agencies securities
Contractual maturities of investments in debt securities available-for-sale, Amortized Cost
Total debt securities available-for-sale	675,940	610,195
Contractual maturities of investments in debt securities available-for-sale, Fair Value
Total debt securities available-for-sale	678,405	619,482
U.S. States and political subdivisions securities
Contractual maturities of investments in debt securities available-for-sale, Amortized Cost
Total debt securities available-for-sale	84,472	78,812
Contractual maturities of investments in debt securities available-for-sale, Fair Value
Total debt securities available-for-sale	85,669	81,127
Mortgage-backed securities - Federal agencies
Contractual maturities of investments in debt securities available-for-sale, Amortized Cost
Total debt securities available-for-sale	484,888	442,748
Contractual maturities of investments in debt securities available-for-sale, Fair Value
Total debt securities available-for-sale	489,490	453,789
Corporate debt securities
Contractual maturities of investments in debt securities available-for-sale, Amortized Cost
Total debt securities available-for-sale	35,800	40,813
Contractual maturities of investments in debt securities available-for-sale, Fair Value
Total debt securities available-for-sale	37,076	42,369
Foreign government and other securities
Contractual maturities of investments in debt securities available-for-sale, Amortized Cost
Total debt securities available-for-sale	700	700
Contractual maturities of investments in debt securities available-for-sale, Fair Value
Total debt securities available-for-sale	$ 700	$ 700