Investment Securities - Amortized Cost and Fair Value of Securities Available-for-Sale (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024	Mar. 31, 2024	Dec. 31, 2023
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 3,299,245	$ 3,410,272
Allowance for Credit Losses	(2,195)	(2,195)	$ (2,525)	$ (2,525)
Net Carrying Amount	3,297,050	3,408,077
Gross Unrealized Gains	3,763	3,166
Gross Unrealized (Losses)	(297,493)	(338,604)
Estimated Fair Value	3,003,320	3,072,639
U.S. government-sponsored enterprises
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	283,960	297,698
Allowance for Credit Losses	0	0
Net Carrying Amount	283,960	297,698
Gross Unrealized Gains	1,216	1,164
Gross Unrealized (Losses)	(11,520)	(14,072)
Estimated Fair Value	273,656	284,790
U.S. government-sponsored mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,467,153	1,527,463
Allowance for Credit Losses	0	0
Net Carrying Amount	1,467,153	1,527,463
Gross Unrealized Gains	931	760
Gross Unrealized (Losses)	(169,526)	(203,539)
Estimated Fair Value	1,298,558	1,324,684
Private mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	181,859	184,643
Allowance for Credit Losses	0	0
Net Carrying Amount	181,859	184,643
Gross Unrealized Gains	19	0
Gross Unrealized (Losses)	(10,541)	(13,249)
Estimated Fair Value	171,337	171,394
Non-government-sponsored asset backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	202,999	228,751
Allowance for Credit Losses	0
Net Carrying Amount	202,999	228,751
Gross Unrealized Gains	204	331
Gross Unrealized (Losses)	(2,772)	(3,434)
Estimated Fair Value	200,431	225,648
State and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	947,565	956,055
Allowance for Credit Losses	0	0
Net Carrying Amount	947,565	956,055
Gross Unrealized Gains	350	335
Gross Unrealized (Losses)	(87,861)	(86,029)
Estimated Fair Value	860,054	870,361
Other securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	215,709	215,662
Allowance for Credit Losses	(2,195)	(2,195)
Net Carrying Amount	213,514	213,467
Gross Unrealized Gains	1,043	576
Gross Unrealized (Losses)	(15,273)	(18,281)
Estimated Fair Value	$ 199,284	$ 195,762

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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