Investment Securities - Maturities of Investment Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Investments, Debt and Equity Securities [Abstract]
Held-to-maturity, amortized cost, one year or less	$ 1,915
Held-to-maturity, amortized cost, after one through five years	10,313
Held-to-maturity, amortized cost, after five through ten years	363,981
Held-to-maturity, amortized cost, after ten years	2,190,641
Held-to-maturity, amortized cost, securities not due on a single maturity date	1,193,118
Amortized Cost	3,759,968	$ 3,761,094
Held-to-maturity, fair value, one year or less	1,909
Held-to-maturity, fair value, after one through five years	9,857
Held-to-maturity, fair value, after five through ten years	315,452
Held-to-maturity, fair value, after ten years	1,693,250
Held-to-maturity, fair value, securities not due on a single maturity date	1,074,390
Held-to-maturity, fair value, total	3,094,858	3,063,233
Available-for-sale, amortized cost, one year or less	64,701
Available-for-sale, amortized cost, after one through five years	166,086
Available-for-sale, amortized cost, after five through ten years	218,164
Available-for-sale, amortized cost, after ten years	1,030,810
Available-for-sale, amortized cost, securities not due on a single maturity date	2,532,234
Available-for-sale, amortized cost, other securities (no maturity)	270
Amortized Cost	4,012,265	4,331,413
Available-for-sale, fair value, one year or less	63,160
Available-for-sale, fair value, after one through five years	160,826
Available-for-sale, fair value, after five through ten years	187,975
Available-for-sale, fair value, after ten years	885,199
Available-for-sale, fair value, securities not due on a single maturity date	2,282,328
Available-for-sale, fair value, other securities (no maturity)	270
Available-for-sale, fair value, total	$ 3,579,758	$ 3,852,854