Investment Securities - Summary of Investment Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Held-to-maturity
Amortized Cost	$ 3,639,850	$ 3,729,502
Allowance for Credit Losses	(3,214)	(3,214)	$ (1,388)
Net Carrying Amount	3,636,636	3,726,288
Gross Unrealized Gains	232	638
Gross Unrealized (Losses)	(686,917)	(591,556)
Estimated Fair Value	2,949,951	3,135,370
Available-for-sale
Amortized Cost	2,852,774	3,509,709
Allowance for Credit Losses	0	0	0
Gross Unrealized Gains	307	230
Gross Unrealized (Losses)	(323,655)	(357,786)
Estimated Fair Value	2,529,426	3,152,153
U.S. Treasury
Available-for-sale
Amortized Cost	999	2,285
Allowance for Credit Losses	0	0
Gross Unrealized Gains	0	0
Gross Unrealized (Losses)	(3)	(31)
Estimated Fair Value	996	2,254
U.S. Government agencies
Held-to-maturity
Amortized Cost	455,869	453,121
Allowance for Credit Losses	0	0
Net Carrying Amount	455,869	453,121
Gross Unrealized Gains	0	0
Gross Unrealized (Losses)	(95,961)	(89,203)
Estimated Fair Value	359,908	363,918
Available-for-sale
Amortized Cost	55,589	74,460
Allowance for Credit Losses	0	0
Gross Unrealized Gains	5	35
Gross Unrealized (Losses)	(1,047)	(1,993)
Estimated Fair Value	54,547	72,502
Mortgage-backed securities
Held-to-maturity
Amortized Cost	1,070,032	1,161,694
Allowance for Credit Losses	0	0
Net Carrying Amount	1,070,032	1,161,694
Gross Unrealized Gains	212	354
Gross Unrealized (Losses)	(133,746)	(107,834)
Estimated Fair Value	936,498	1,054,214
Available-for-sale
Amortized Cost	1,545,539	2,138,652
Allowance for Credit Losses	0	0
Gross Unrealized Gains	4	8
Gross Unrealized (Losses)	(152,784)	(198,353)
Estimated Fair Value	1,392,759	1,940,307
State and political subdivisions
Held-to-maturity
Amortized Cost	1,857,373	1,858,680
Allowance for Credit Losses	(196)	(2,006)	(110)
Net Carrying Amount	1,857,177	1,856,674
Gross Unrealized Gains	20	284
Gross Unrealized (Losses)	(436,061)	(369,509)
Estimated Fair Value	1,421,136	1,487,449
Available-for-sale
Amortized Cost	1,015,619	1,035,147
Allowance for Credit Losses	0	0	0
Gross Unrealized Gains	132	187
Gross Unrealized (Losses)	(157,569)	(132,541)
Estimated Fair Value	858,182	902,793
Other securities
Held-to-maturity
Amortized Cost	256,576	256,007
Allowance for Credit Losses	(3,018)	(1,208)	(1,278)
Net Carrying Amount	253,558	254,799
Gross Unrealized Gains	0	0
Gross Unrealized (Losses)	(21,149)	(25,010)
Estimated Fair Value	232,409	229,789
Available-for-sale
Amortized Cost	235,028	259,165
Allowance for Credit Losses	0	0	$ 0
Gross Unrealized Gains	166	0
Gross Unrealized (Losses)	(12,252)	(24,868)
Estimated Fair Value	$ 222,942	$ 234,297

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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