Investment Securities - Amortized Cost and Fair Value of Available-for-Sale Investment Securities Portfolio (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Available-for-Sale
Total	$ 7,551,258	$ 7,772,603
Unrealized Gains	1,084	3,028
Unrealized Losses	(935,766)	(847,474)
Basis adjustments	(116,061)	(154,445)
Fair Value	6,500,515	6,773,712
Held-to-Maturity
Allowance for securities held-to-maturity	(150)	(150)
Total held-to-maturity securities	3,054,997	3,089,147
Unrealized Gains	437	221
Unrealized Losses	(452,376)	(445,686)
Basis adjustments	0	0
Fair Value	2,603,058	2,643,682
U.S. Treasury
Available-for-Sale
Total	364,824	253,148
Unrealized Gains	0	5
Unrealized Losses	(9,245)	(5,189)
Basis adjustments	(43,167)	(47,037)
Fair Value	312,412	200,927
U.S. government-sponsored entities and agencies
Available-for-Sale
Total	1,448,873	1,451,736
Unrealized Gains	0	0
Unrealized Losses	(201,623)	(169,248)
Basis adjustments	(72,894)	(107,408)
Fair Value	1,174,356	1,175,080
Held-to-Maturity
Amortized Cost	822,517	819,168
Unrealized Gains	0	0
Unrealized Losses	(167,071)	(162,810)
Basis adjustments	0	0
Fair Value	655,446	656,358
Mortgage-backed securities
Available-for-Sale
Total	4,760,921	4,986,354
Unrealized Gains	123	976
Unrealized Losses	(663,273)	(617,428)
Basis adjustments	0	0
Fair Value	4,097,771	4,369,902
Held-to-Maturity
Amortized Cost	1,070,687	1,106,817
Unrealized Gains	0	0
Unrealized Losses	(142,191)	(123,854)
Basis adjustments	0	0
Fair Value	928,496	982,963
States and political subdivisions
Available-for-Sale
Total	623,196	688,159
Unrealized Gains	844	1,789
Unrealized Losses	(25,258)	(26,096)
Basis adjustments	0	0
Fair Value	598,782	663,852
Held-to-Maturity
Amortized Cost	1,161,943	1,163,312
Unrealized Gains	437	221
Unrealized Losses	(143,114)	(159,022)
Basis adjustments	0	0
Fair Value	1,019,266	1,004,511
Pooled trust preferred securities
Available-for-Sale
Total	13,791	13,783
Unrealized Gains	0	0
Unrealized Losses	(2,797)	(2,972)
Basis adjustments	0	0
Fair Value	10,994	10,811
Other securities
Available-for-Sale
Total	339,653	379,423
Unrealized Gains	117	258
Unrealized Losses	(33,570)	(26,541)
Basis adjustments	0	0
Fair Value	$ 306,200	$ 353,140

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

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