Investment Securities - Amortized Cost and Fair Value of Available-for-Sale Investment Securities Portfolio (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Available-for-Sale
Amortized Cost	$ 7,684,889	$ 7,772,603
Unrealized Gains	4,607	3,028
Unrealized Losses	(874,143)	(847,474)
Basis Adjustments	(102,298)	(154,445)
Fair Value	6,713,055	6,773,712
Held-to-Maturity
Allowance for securities held-to-maturity	(150)	(150)
Total held-to-maturity securities	3,013,493	3,089,147
Unrealized Gains	1,800	221
Unrealized Losses	(414,105)	(445,686)
Basis adjustments	0	0
Investment securities-held-to-maturity, fair value	2,601,188	2,643,682
U.S. Treasury
Available-for-Sale
Amortized Cost	449,817	253,148
Unrealized Gains	154	5
Unrealized Losses	(11,941)	(5,189)
Basis Adjustments	(41,297)	(47,037)
Fair Value	396,733	200,927
U.S. government-sponsored entities and agencies
Available-for-Sale
Amortized Cost	1,487,879	1,451,736
Unrealized Gains	33	0
Unrealized Losses	(192,717)	(169,248)
Basis Adjustments	(63,931)	(107,408)
Fair Value	1,231,264	1,175,080
Held-to-Maturity
Amortized Cost	825,953	819,168
Unrealized Gains	0	0
Unrealized Losses	(154,827)	(162,810)
Basis adjustments	0	0
Investment securities-held-to-maturity, fair value	671,126	656,358
Mortgage-backed securities
Available-for-Sale
Amortized Cost	4,835,319	4,986,354
Unrealized Gains	3,093	976
Unrealized Losses	(621,852)	(617,428)
Basis Adjustments	0	0
Fair Value	4,216,560	4,369,902
Held-to-Maturity
Amortized Cost	1,029,131	1,106,817
Unrealized Gains	0	0
Unrealized Losses	(147,137)	(123,854)
Basis adjustments	0	0
Investment securities-held-to-maturity, fair value	881,994	982,963
States and political subdivisions
Available-for-Sale
Amortized Cost	554,509	688,159
Unrealized Gains	878	1,789
Unrealized Losses	(23,057)	(26,096)
Basis Adjustments	2,930	0
Fair Value	535,260	663,852
Held-to-Maturity
Amortized Cost	1,158,559	1,163,312
Unrealized Gains	1,800	221
Unrealized Losses	(112,141)	(159,022)
Basis adjustments	0	0
Investment securities-held-to-maturity, fair value	1,048,218	1,004,511
Pooled trust preferred securities
Available-for-Sale
Amortized Cost	13,797	13,783
Unrealized Gains	0	0
Unrealized Losses	(2,460)	(2,972)
Basis Adjustments	0	0
Fair Value	11,337	10,811
Other securities
Available-for-Sale
Amortized Cost	343,568	379,423
Unrealized Gains	449	258
Unrealized Losses	(22,116)	(26,541)
Basis Adjustments	0	0
Fair Value	$ 321,901	$ 353,140

Debt Securities, Available-For-Sale, Accumulated Basis Adjustments, Before Tax

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Debt Securities, Held-To-Maturity, Accumulated Basis Adjustments, Before Tax

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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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