Investment Securities - Amortized Cost and Fair Value of Securities Available-for-Sale (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023	Jun. 30, 2023	Dec. 31, 2022
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 3,691,868	$ 3,840,927
Allowance for Credit Losses	(2,525)	(2,525)	$ (2,525)	$ (842)
Net Carrying Amount	3,689,343	3,838,402
Gross Unrealized Gains	3,922	5,718
Gross Unrealized (Losses)	(348,726)	(336,279)
Estimated Fair Value	3,344,539	3,507,841
U.S. government-sponsored enterprises
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	334,736	361,494
Allowance for Credit Losses	0	0
Net Carrying Amount	334,736	361,494
Gross Unrealized Gains	1,626	2,247
Gross Unrealized (Losses)	(16,869)	(17,093)
Estimated Fair Value	319,493	346,648
U.S. government-sponsored mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,621,192	1,711,668
Allowance for Credit Losses	0	0
Net Carrying Amount	1,621,192	1,711,668
Gross Unrealized Gains	547	310
Gross Unrealized (Losses)	(201,264)	(191,557)
Estimated Fair Value	1,420,475	1,520,421
Private mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	188,551	191,522
Allowance for Credit Losses	0	0
Net Carrying Amount	188,551	191,522
Gross Unrealized Gains	0	0
Gross Unrealized (Losses)	(15,418)	(16,117)
Estimated Fair Value	173,133	175,405
Non-government-sponsored asset backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	358,968	370,203
Allowance for Credit Losses	0
Net Carrying Amount	358,968	370,203
Gross Unrealized Gains	700	821
Gross Unrealized (Losses)	(5,869)	(7,551)
Estimated Fair Value	353,799	363,473
State and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	972,688	990,318
Allowance for Credit Losses	0	0
Net Carrying Amount	972,688	990,318
Gross Unrealized Gains	583	1,938
Gross Unrealized (Losses)	(83,006)	(75,931)
Estimated Fair Value	890,265	916,325
Other securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	215,733	215,722
Allowance for Credit Losses	(2,525)	(2,525)
Net Carrying Amount	213,208	213,197
Gross Unrealized Gains	466	402
Gross Unrealized (Losses)	(26,300)	(28,030)
Estimated Fair Value	$ 187,374	$ 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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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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