Investment Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Contractual maturities of investments in debt securities available-for-sale, Amortized Cost
Due in one year or less	$ 104,525
Due after one year through five years	633,313
Due after five years through ten years	146,985
Due after ten years	470
Mortgage-backed securities	517,713
Total debt securities available-for-sale	1,403,006	$ 1,173,268
Contractual maturities of investments in debt securities available-for-sale, Fair Value
Due in one year or less	105,576
Due after one year through five years	638,184
Due after five years through ten years	145,918
Due after ten years	449
Mortgage-backed securities	522,895
Total debt securities available-for-sale	1,413,022	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	767,147	610,195
Contractual maturities of investments in debt securities available-for-sale, Fair Value
Total debt securities available-for-sale	769,878	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	89,938	78,812
Contractual maturities of investments in debt securities available-for-sale, Fair Value
Total debt securities available-for-sale	91,135	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	517,713	442,748
Contractual maturities of investments in debt securities available-for-sale, Fair Value
Total debt securities available-for-sale	522,895	453,789
Corporate debt securities
Contractual maturities of investments in debt securities available-for-sale, Amortized Cost
Total debt securities available-for-sale	27,508	40,813
Contractual maturities of investments in debt securities available-for-sale, Fair Value
Total debt securities available-for-sale	28,414	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