Investment Securities - Amortized Cost and Fair Value of Available-for-Sale Investment Securities Portfolio (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Available-for-Sale
Total	$ 7,834,082	$ 7,684,889
Unrealized Gains	2,810	4,607
Unrealized Losses	(917,039)	(874,143)
Basis adjustments	(128,201)	(102,298)
Fair Value	6,791,652	6,713,055
Held-to-Maturity
Allowance for securities held-to-maturity	(150)	(150)
Total held-to-maturity securities	3,001,349	3,013,493
Unrealized Gains	864	1,800
Unrealized Losses	(454,637)	(414,105)
Basis adjustments	0	0
Fair Value	2,547,576	2,601,188
U.S. Treasury
Available-for-Sale
Total	291,538	449,817
Unrealized Gains	19	154
Unrealized Losses	(9,956)	(11,941)
Basis adjustments	(48,550)	(41,297)
Fair Value	233,051	396,733
U.S. government-sponsored entities and agencies
Available-for-Sale
Total	1,448,561	1,487,879
Unrealized Gains	0	33
Unrealized Losses	(184,941)	(192,717)
Basis adjustments	(80,601)	(63,931)
Fair Value	1,183,019	1,231,264
Held-to-Maturity
Amortized Cost	827,684	825,953
Unrealized Gains	0	0
Unrealized Losses	(164,949)	(154,827)
Basis adjustments	0	0
Fair Value	662,735	671,126
Mortgage-backed securities
Available-for-Sale
Total	5,223,119	4,835,319
Unrealized Gains	1,996	3,093
Unrealized Losses	(675,092)	(621,852)
Basis adjustments	0	0
Fair Value	4,550,023	4,216,560
Held-to-Maturity
Amortized Cost	1,016,858	1,029,131
Unrealized Gains	0	0
Unrealized Losses	(159,201)	(147,137)
Basis adjustments	0	0
Fair Value	857,657	881,994
States and political subdivisions
Available-for-Sale
Total	537,930	554,509
Unrealized Gains	404	878
Unrealized Losses	(24,180)	(23,057)
Basis adjustments	950	2,930
Fair Value	515,104	535,260
Held-to-Maturity
Amortized Cost	1,156,957	1,158,559
Unrealized Gains	864	1,800
Unrealized Losses	(130,487)	(112,141)
Basis adjustments	0	0
Fair Value	1,027,334	1,048,218
Pooled trust preferred securities
Available-for-Sale
Total	13,800	13,797
Unrealized Gains	0	0
Unrealized Losses	(2,526)	(2,460)
Basis adjustments	0	0
Fair Value	11,274	11,337
Other securities
Available-for-Sale
Total	319,134	343,568
Unrealized Gains	391	449
Unrealized Losses	(20,344)	(22,116)
Basis adjustments	0	0
Fair Value	$ 299,181	$ 321,901

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

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