Investment Securities - Amortized Cost and Fair Value of Securities Available-for-Sale (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025	Mar. 31, 2025	Dec. 31, 2024
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 3,038,388	$ 3,088,820
Allowance for Credit Losses	0	0	$ (2,195)	$ (2,195)
Net Carrying Amount	3,038,388	3,088,820
Gross Unrealized Gains	4,951	6,493
Gross Unrealized (Losses)	(239,492)	(223,382)
Estimated Fair Value	2,803,847	2,871,931
U.S. government-sponsored enterprises
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	225,306	246,891
Allowance for Credit Losses	0	0
Net Carrying Amount	225,306	246,891
Gross Unrealized Gains	1,054	998
Gross Unrealized (Losses)	(7,389)	(7,107)
Estimated Fair Value	218,971	240,782
U.S. government-sponsored mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,320,400	1,345,469
Allowance for Credit Losses	0	0
Net Carrying Amount	1,320,400	1,345,469
Gross Unrealized Gains	1,293	1,478
Gross Unrealized (Losses)	(143,819)	(133,999)
Estimated Fair Value	1,177,874	1,212,948
Private mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	150,637	152,578
Allowance for Credit Losses	0	0
Net Carrying Amount	150,637	152,578
Gross Unrealized Gains	0	126
Gross Unrealized (Losses)	(8,110)	(6,984)
Estimated Fair Value	142,527	145,720
Non-government-sponsored asset backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	155,852	158,446
Allowance for Credit Losses	0	0
Net Carrying Amount	155,852	158,446
Gross Unrealized Gains	111	325
Gross Unrealized (Losses)	(1,137)	(927)
Estimated Fair Value	154,826	157,844
State and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	949,052	951,822
Allowance for Credit Losses	0	0
Net Carrying Amount	949,052	951,822
Gross Unrealized Gains	665	1,419
Gross Unrealized (Losses)	(70,739)	(65,403)
Estimated Fair Value	878,978	887,838
Other securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	237,141	233,614
Allowance for Credit Losses	0	0
Net Carrying Amount	237,141	233,614
Gross Unrealized Gains	1,828	2,147
Gross Unrealized (Losses)	(8,298)	(8,962)
Estimated Fair Value	$ 230,671	$ 226,799

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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Amount, before tax, of unrealized loss 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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Amortized cost excluding accrued interest, after allowance for credit loss, of 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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