Investment Securities - Amortized Cost and Fair Value of Available-for-Sale Investment Securities Portfolio (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Available-for-Sale
Total	$ 8,168,508	$ 7,684,889
Unrealized Gains	2,589	4,607
Unrealized Losses	(934,608)	(874,143)
Basis adjustments	(131,011)	(102,298)
Fair Value	7,105,478	6,713,055
Held-to-Maturity
Allowance for securities held-to-maturity	(150)	(150)
Total held-to-maturity securities	2,986,449	3,013,493
Unrealized Gains	469	1,800
Unrealized Losses	(474,416)	(414,105)
Basis adjustments	0	0
Fair Value	2,512,502	2,601,188
U.S. Treasury
Available-for-Sale
Total	265,745	449,817
Unrealized Gains	8	154
Unrealized Losses	(10,940)	(11,941)
Basis adjustments	(49,505)	(41,297)
Fair Value	205,308	396,733
U.S. government-sponsored entities and agencies
Available-for-Sale
Total	1,442,132	1,487,879
Unrealized Gains	0	33
Unrealized Losses	(187,768)	(192,717)
Basis adjustments	(82,070)	(63,931)
Fair Value	1,172,294	1,231,264
Held-to-Maturity
Amortized Cost	829,402	825,953
Unrealized Gains	0	0
Unrealized Losses	(167,071)	(154,827)
Basis adjustments	0	0
Fair Value	662,331	671,126
Mortgage-backed securities
Available-for-Sale
Total	5,571,763	4,835,319
Unrealized Gains	2,244	3,093
Unrealized Losses	(685,551)	(621,852)
Basis adjustments	0	0
Fair Value	4,888,456	4,216,560
Held-to-Maturity
Amortized Cost	1,001,915	1,029,131
Unrealized Gains	0	0
Unrealized Losses	(163,626)	(147,137)
Basis adjustments	0	0
Fair Value	838,289	881,994
States and political subdivisions
Available-for-Sale
Total	550,897	554,509
Unrealized Gains	121	878
Unrealized Losses	(28,267)	(23,057)
Basis adjustments	564	2,930
Fair Value	523,315	535,260
Held-to-Maturity
Amortized Cost	1,155,282	1,158,559
Unrealized Gains	469	1,800
Unrealized Losses	(143,719)	(112,141)
Basis adjustments	0	0
Fair Value	1,012,032	1,048,218
Pooled trust preferred securities
Available-for-Sale
Total	13,802	13,797
Unrealized Gains	0	0
Unrealized Losses	(2,504)	(2,460)
Basis adjustments	0	0
Fair Value	11,298	11,337
Other securities
Available-for-Sale
Total	324,169	343,568
Unrealized Gains	216	449
Unrealized Losses	(19,578)	(22,116)
Basis adjustments	0	0
Fair Value	$ 304,807	$ 321,901

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

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