Debt Securities - Amortized Cost, Gross Unrealized Gains and Losses and Fair Value of Investment Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024
Available-for-sale
Amortized Cost	$ 4,522,652	$ 4,656,310
Gross Unrealized Gains	374	227
Gross Unrealized Losses	(350,714)	(411,332)
Fair Value	4,172,312	4,245,205
Held-to-maturity
Amortized Cost	3,261,575	3,294,847
Gross Unrealized Gains	815	810
Gross Unrealized Losses	(308,967)	(327,087)
Fair Value	2,953,423	2,968,570
Total debt securities
Amortized Cost	7,784,227	7,951,157
Gross Unrealized Gains	1,189	1,037
Gross Unrealized Losses	(659,681)	(738,419)
Fair Value	7,125,735	7,213,775
U.S. government and federal agency
Available-for-sale
Amortized Cost	483,984	484,082
Gross Unrealized Gains	9	5
Gross Unrealized Losses	(11,871)	(15,654)
Fair Value	472,122	468,433
Held-to-maturity
Amortized Cost	860,978	859,432
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(44,125)	(54,496)
Fair Value	816,853	804,936
U.S. government sponsored enterprises
Available-for-sale
Amortized Cost	324,323	323,854
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(10,815)	(13,700)
Fair Value	313,508	310,154
State and local governments
Available-for-sale
Amortized Cost	70,803	71,737
Gross Unrealized Gains	225	215
Gross Unrealized Losses	(3,111)	(3,272)
Fair Value	67,917	68,680
Held-to-maturity
Amortized Cost	1,613,709	1,619,850
Gross Unrealized Gains	810	810
Gross Unrealized Losses	(212,791)	(209,502)
Fair Value	1,401,728	1,411,158
Corporate bonds
Available-for-sale
Amortized Cost	14,797	14,818
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(145)	(315)
Fair Value	14,652	14,503
Residential mortgage-backed securities
Available-for-sale
Amortized Cost	2,541,431	2,660,330
Gross Unrealized Gains	7	5
Gross Unrealized Losses	(263,017)	(304,819)
Fair Value	2,278,421	2,355,516
Held-to-maturity
Amortized Cost	786,888	815,565
Gross Unrealized Gains	5	0
Gross Unrealized Losses	(52,051)	(63,089)
Fair Value	734,842	752,476
Commercial mortgage-backed securities
Available-for-sale
Amortized Cost	1,087,314	1,101,489
Gross Unrealized Gains	133	2
Gross Unrealized Losses	(61,755)	(73,572)
Fair Value	$ 1,025,692	$ 1,027,919