Investment Securities - Maturities of Investment Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Investments, Debt and Equity Securities [Abstract]
Held-to-maturity, amortized cost, one year or less	$ 1,570
Held-to-maturity, amortized cost, after one through five years	13,708
Held-to-maturity, amortized cost, after five through ten years	394,392
Held-to-maturity, amortized cost, after ten years	2,158,450
Held-to-maturity, amortized cost, securities not due on a single maturity date	1,142,352
Amortized Cost	3,710,472	$ 3,729,502
Held-to-maturity, fair value, one year or less	1,516
Held-to-maturity, fair value, after one through five years	13,065
Held-to-maturity, fair value, after five through ten years	347,677
Held-to-maturity, fair value, after ten years	1,670,987
Held-to-maturity, fair value, securities not due on a single maturity date	1,016,037
Held-to-maturity, fair value, total	3,049,282	3,135,370
Available-for-sale, amortized cost, one year or less	10,034
Available-for-sale, amortized cost, after one through five years	116,012
Available-for-sale, amortized cost, after five through ten years	213,380
Available-for-sale, amortized cost, after ten years	1,006,399
Available-for-sale, amortized cost, securities not due on a single maturity date	2,048,895
Available-for-sale, amortized cost, other securities (no maturity)	251
Amortized Cost	3,394,971	3,509,709
Available-for-sale, fair value, one year or less	9,778
Available-for-sale, fair value, after one through five years	115,248
Available-for-sale, fair value, after five through ten years	188,442
Available-for-sale, fair value, after ten years	868,475
Available-for-sale, fair value, securities not due on a single maturity date	1,845,364
Available-for-sale, fair value, other securities (no maturity)	251
Available-for-sale, fair value, total	$ 3,027,558	$ 3,152,153