Investment Securities - Amortized Cost and Fair Value of Securities Available-for-Sale (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023	Sep. 30, 2023	Dec. 31, 2022
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 3,529,325	$ 3,840,927
Allowance for Credit Losses	(2,195)	(2,525)	$ (2,525)	$ (842)
Net Carrying Amount	3,527,130	3,838,402
Gross Unrealized Gains	5,299	5,718
Gross Unrealized (Losses)	(261,809)	(336,279)
Estimated Fair Value	3,270,620	3,507,841
U.S. government-sponsored enterprises
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	321,233	361,494
Allowance for Credit Losses	0	0
Net Carrying Amount	321,233	361,494
Gross Unrealized Gains	1,800	2,247
Gross Unrealized (Losses)	(11,248)	(17,093)
Estimated Fair Value	311,785	346,648
U.S. government-sponsored mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,574,430	1,711,668
Allowance for Credit Losses	0	0
Net Carrying Amount	1,574,430	1,711,668
Gross Unrealized Gains	1,105	310
Gross Unrealized (Losses)	(150,070)	(191,557)
Estimated Fair Value	1,425,465	1,520,421
Private mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	186,916	191,522
Allowance for Credit Losses	0	0
Net Carrying Amount	186,916	191,522
Gross Unrealized Gains	115	0
Gross Unrealized (Losses)	(9,090)	(16,117)
Estimated Fair Value	177,941	175,405
Non-government-sponsored asset backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	264,497	370,203
Allowance for Credit Losses	0
Net Carrying Amount	264,497	370,203
Gross Unrealized Gains	646	821
Gross Unrealized (Losses)	(2,945)	(7,551)
Estimated Fair Value	262,198	363,473
State and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	966,644	990,318
Allowance for Credit Losses	0	0
Net Carrying Amount	966,644	990,318
Gross Unrealized Gains	1,094	1,938
Gross Unrealized (Losses)	(66,804)	(75,931)
Estimated Fair Value	900,934	916,325
Other securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	215,605	215,722
Allowance for Credit Losses	(2,195)	(2,525)
Net Carrying Amount	213,410	213,197
Gross Unrealized Gains	539	402
Gross Unrealized (Losses)	(21,652)	(28,030)
Estimated Fair Value	$ 192,297	$ 185,569

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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