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Investment Securities - Available-for-Sale and Held-to-Maturity Investment Securities with Unrealized Losses by Aggregated Major Security Type and Length of Time in Continuous Unrealized Loss Position (Details) - USD ($) $ in Thousands	Jun. 30, 2025	Dec. 31, 2024
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-Sale, Less than 12 months, Fair Value	$ 579,672	$ 1,126,895
Available-for-Sale, Less than 12 months, Unrealized Losses	(3,806)	(12,668)
Available-for-Sale, 12 months or longer, Fair Value	5,096,698	5,218,733
Available-for-Sale, 12 months or longer, Unrealized Losses	(761,706)	(884,848)
Available-for-Sale, Fair Value	5,676,370	6,345,628
Available-for-Sale, Unrealized Losses	(765,512)	(897,516)
U.S. Treasury
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-Sale, Less than 12 months, Fair Value	2,992	3,977
Available-for-Sale, Less than 12 months, Unrealized Losses	(9)	(26)
Available-for-Sale, 12 months or longer, Fair Value	180,172	177,691
Available-for-Sale, 12 months or longer, Unrealized Losses	(11,814)	(12,633)
Available-for-Sale, Fair Value	183,164	181,668
Available-for-Sale, Unrealized Losses	(11,823)	(12,659)
U.S. government-sponsored entities and agencies
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-Sale, Less than 12 months, Fair Value	107,447	98,280
Available-for-Sale, Less than 12 months, Unrealized Losses	(796)	(1,713)
Available-for-Sale, 12 months or longer, Fair Value	1,158,392	1,144,618
Available-for-Sale, 12 months or longer, Unrealized Losses	(158,402)	(179,647)
Available-for-Sale, Fair Value	1,265,839	1,242,898
Available-for-Sale, Unrealized Losses	(159,198)	(181,360)
Mortgage-backed securities
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-Sale, Less than 12 months, Fair Value	372,714	857,440
Available-for-Sale, Less than 12 months, Unrealized Losses	(2,174)	(9,172)
Available-for-Sale, 12 months or longer, Fair Value	3,309,123	3,406,350
Available-for-Sale, 12 months or longer, Unrealized Losses	(552,699)	(653,009)
Available-for-Sale, Fair Value	3,681,837	4,263,790
Available-for-Sale, Unrealized Losses	(554,873)	(662,181)
States and political subdivisions
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-Sale, Less than 12 months, Fair Value	70,158	133,906
Available-for-Sale, Less than 12 months, Unrealized Losses	(720)	(1,462)
Available-for-Sale, 12 months or longer, Fair Value	258,259	279,121
Available-for-Sale, 12 months or longer, Unrealized Losses	(27,797)	(24,419)
Available-for-Sale, Fair Value	328,417	413,027
Available-for-Sale, Unrealized Losses	(28,517)	(25,881)
Pooled trust preferred securities
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-Sale, Less than 12 months, Fair Value	0	0
Available-for-Sale, Less than 12 months, Unrealized Losses	0	0
Available-for-Sale, 12 months or longer, Fair Value	11,319	11,322
Available-for-Sale, 12 months or longer, Unrealized Losses	(2,494)	(2,485)
Available-for-Sale, Fair Value	11,319	11,322
Available-for-Sale, Unrealized Losses	(2,494)	(2,485)
Other securities
Debt Securities, Available-for-sale, Unrealized Loss Position [Line Items]
Available-for-Sale, Less than 12 months, Fair Value	26,361	33,292
Available-for-Sale, Less than 12 months, Unrealized Losses	(107)	(295)
Available-for-Sale, 12 months or longer, Fair Value	179,433	199,631
Available-for-Sale, 12 months or longer, Unrealized Losses	(8,500)	(12,655)
Available-for-Sale, Fair Value	205,794	232,923
Available-for-Sale, Unrealized Losses	$ (8,607)	$ (12,950)

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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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