Investment Securities - Amortized Cost and Fair Value of Available-for-Sale Investment Securities Portfolio (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Available-for-Sale
Total	$ 7,592,765	$ 7,772,603
Unrealized Gains	3,090	3,028
Unrealized Losses	(817,596)	(847,474)
Basis adjustments	(91,193)	(154,445)
Fair Value	6,687,066	6,773,712
Held-to-Maturity
Allowance for securities held-to-maturity	(150)	(150)
Total held-to-maturity securities	3,071,190	3,089,147
Unrealized Gains	744	221
Unrealized Losses	(408,560)	(445,686)
Basis adjustments	0	0
Fair Value	2,663,374	2,643,682
U.S. Treasury
Available-for-Sale
Total	268,894	253,148
Unrealized Gains	34	5
Unrealized Losses	(10,755)	(5,189)
Basis adjustments	(36,301)	(47,037)
Fair Value	221,872	200,927
U.S. government-sponsored entities and agencies
Available-for-Sale
Total	1,450,300	1,451,736
Unrealized Gains	0	0
Unrealized Losses	(201,717)	(169,248)
Basis adjustments	(54,892)	(107,408)
Fair Value	1,193,691	1,175,080
Held-to-Maturity
Amortized Cost	820,849	819,168
Unrealized Gains	0	0
Unrealized Losses	(157,226)	(162,810)
Basis adjustments	0	0
Fair Value	663,623	656,358
Mortgage-backed securities
Available-for-Sale
Total	4,861,624	4,986,354
Unrealized Gains	641	976
Unrealized Losses	(553,490)	(617,428)
Basis adjustments	0	0
Fair Value	4,308,775	4,369,902
Held-to-Maturity
Amortized Cost	1,086,905	1,106,817
Unrealized Gains	0	0
Unrealized Losses	(113,419)	(123,854)
Basis adjustments	0	0
Fair Value	973,486	982,963
States and political subdivisions
Available-for-Sale
Total	641,317	688,159
Unrealized Gains	2,138	1,789
Unrealized Losses	(21,968)	(26,096)
Basis adjustments	0	0
Fair Value	621,487	663,852
Held-to-Maturity
Amortized Cost	1,163,586	1,163,312
Unrealized Gains	744	221
Unrealized Losses	(137,915)	(159,022)
Basis adjustments	0	0
Fair Value	1,026,415	1,004,511
Pooled trust preferred securities
Available-for-Sale
Total	13,787	13,783
Unrealized Gains	0	0
Unrealized Losses	(2,938)	(2,972)
Basis adjustments	0	0
Fair Value	10,849	10,811
Other securities
Available-for-Sale
Total	356,843	379,423
Unrealized Gains	277	258
Unrealized Losses	(26,728)	(26,541)
Basis adjustments	0	0
Fair Value	$ 330,392	$ 353,140

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

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