Investment Securities - Maturities of Investment Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Held-to-maturity, amortized cost, one year or less	$ 4,331
Held-to-maturity, amortized cost, after one through five years	4,213
Held-to-maturity, amortized cost, after five through ten years	28,026
Held-to-maturity, amortized cost, after ten years	1,409,136
Held-to-maturity, amortized cost, securities not due on a single maturity date	112,496
Amortized Cost	1,558,202	$ 1,530,500
Held-to-maturity, fair value, one year or less	4,355
Held-to-maturity, fair value, after one through five years	4,291
Held-to-maturity, fair value, after five through ten years	24,759
Held-to-maturity, fair value, after ten years	1,168,709
Held-to-maturity, fair value, securities not due on a single maturity date	104,944
Held-to-maturity, fair value, total	1,307,058	1,517,378
Available-for-sale, amortized cost, one year or less	6,564
Available-for-sale, amortized cost, after one through five years	65,960
Available-for-sale, amortized cost, after five through ten years	559,472
Available-for-sale, amortized cost, after ten years	2,059,481
Available-for-sale, amortized cost, securities not due on a single maturity date	4,378,489
Available-for-sale, amortized cost, other securities (no maturity)	616
Amortized Cost	7,070,582	7,130,861
Available-for-sale, fair value, one year or less	6,560
Available-for-sale, fair value, after one through five years	64,934
Available-for-sale, fair value, after five through ten years	530,695
Available-for-sale, fair value, after ten years	1,871,156
Available-for-sale, fair value, securities not due on a single maturity date	4,166,108
Available-for-sale, fair value, other securities (no maturity)	616
Available-for-sale, fair value, total	$ 6,640,069	$ 7,113,545