Debt Securities - Amortized Cost, Gross Unrealized Gains and Losses and Fair Value of Investment Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Available-for-sale
Amortized Cost	$ 4,656,310	$ 5,283,253
Gross Unrealized Gains	227	841
Gross Unrealized Losses	(411,332)	(498,375)
Fair Value	4,245,205	4,785,719
Held-to-maturity
Amortized Cost	3,294,847	3,502,411
Gross Unrealized Gains	810	2,843
Gross Unrealized Losses	(327,087)	(325,060)
Fair Value	2,968,570	3,180,194
Total debt securities
Amortized Cost	7,951,157	8,785,664
Gross Unrealized Gains	1,037	3,684
Gross Unrealized Losses	(738,419)	(823,435)
Fair Value	7,213,775	7,965,913
U.S. government and federal agency
Available-for-sale
Amortized Cost	484,082	485,005
Gross Unrealized Gains	5	11
Gross Unrealized Losses	(15,654)	(29,669)
Fair Value	468,433	455,347
Held-to-maturity
Amortized Cost	859,432	853,273
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(54,496)	(65,472)
Fair Value	804,936	787,801
U.S. government sponsored enterprises
Available-for-sale
Amortized Cost	323,854	321,993
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(13,700)	(22,774)
Fair Value	310,154	299,219
State and local governments
Available-for-sale
Amortized Cost	71,737	101,903
Gross Unrealized Gains	215	302
Gross Unrealized Losses	(3,272)	(3,273)
Fair Value	68,680	98,932
Held-to-maturity
Amortized Cost	1,619,850	1,650,000
Gross Unrealized Gains	810	2,843
Gross Unrealized Losses	(209,502)	(181,192)
Fair Value	1,411,158	1,471,651
Corporate bonds
Available-for-sale
Amortized Cost	14,818	27,007
Gross Unrealized Gains	0	2
Gross Unrealized Losses	(315)	(756)
Fair Value	14,503	26,253
Residential mortgage-backed securities
Available-for-sale
Amortized Cost	2,660,330	3,166,589
Gross Unrealized Gains	5	7
Gross Unrealized Losses	(304,819)	(355,333)
Fair Value	2,355,516	2,811,263
Held-to-maturity
Amortized Cost	815,565	999,138
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(63,089)	(78,396)
Fair Value	752,476	920,742
Commercial mortgage-backed securities
Available-for-sale
Amortized Cost	1,101,489	1,180,756
Gross Unrealized Gains	2	519
Gross Unrealized Losses	(73,572)	(86,570)
Fair Value	$ 1,027,919	$ 1,094,705