Investment Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Contractual maturities of investments in debt securities available-for-sale, Amortized Cost
Due in one year or less	$ 127,657
Due after one year through five years	752,143
Due after five years through ten years	129,981
Due after ten years	470
Mortgage-backed securities	569,805
Total debt securities available-for-sale	1,580,056	$ 1,173,268
Contractual maturities of investments in debt securities available-for-sale, Fair Value
Due in one year or less	128,770
Due after one year through five years	754,188
Due after five years through ten years	128,687
Due after ten years	445
Mortgage-backed securities	571,150
Total debt securities available-for-sale	1,583,240	1,197,467
Accrued interest receivable on investment securities available-for-sale	4,520	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	893,378	610,195
Contractual maturities of investments in debt securities available-for-sale, Fair Value
Total debt securities available-for-sale	893,672	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	93,764	78,812
Contractual maturities of investments in debt securities available-for-sale, Fair Value
Total debt securities available-for-sale	94,550	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	569,805	442,748
Contractual maturities of investments in debt securities available-for-sale, Fair Value
Total debt securities available-for-sale	571,150	453,789
Corporate debt securities
Contractual maturities of investments in debt securities available-for-sale, Amortized Cost
Total debt securities available-for-sale	22,509	40,813
Contractual maturities of investments in debt securities available-for-sale, Fair Value
Total debt securities available-for-sale	23,268	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	600	700
Contractual maturities of investments in debt securities available-for-sale, Fair Value
Total debt securities available-for-sale	$ 600	$ 700