Securities - Schedule of Debt Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
AFS debt securities:
Amortized Cost	$ 10,667,293	$ 6,916,491
Gross Unrealized Gains	37,644	783
Gross Unrealized Losses	(571,060)	(728,937)
Fair Value	10,133,877	6,188,337
HTM debt securities:
Amortized Cost	2,928,399	2,956,040
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(418,047)	(502,069)
Fair Value	2,510,352	2,453,971
Total debt securities
Amortized Cost	13,595,692	9,872,531
Gross Unrealized Gains	37,644	783
Gross Unrealized Losses	(989,107)	(1,231,006)
Fair Value	12,644,229	8,642,308
AFS and HTM, accrued interest	40,000	44,000
Government National Mortgage Association (GNMA)
AFS debt securities:
Amortized Cost	6,400,000	1,300,000
Fair Value	6,300,000	1,200,000
HTM debt securities:
Amortized Cost	88,000	92,000
Fair Value	72,000	75,000
U.S. Treasury securities
AFS debt securities:
Amortized Cost	676,294	1,112,587
Gross Unrealized Gains	0	101
Gross Unrealized Losses	(34,721)	(52,313)
Fair Value	641,573	1,060,375
HTM debt securities:
Amortized Cost	533,683	529,548
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(28,539)	(40,997)
Fair Value	505,144	488,551
U.S. government agency and U.S. government-sponsored enterprise debt securities
AFS debt securities:
Amortized Cost	309,277	412,086
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(36,829)	(47,640)
Fair Value	272,448	364,446
HTM debt securities:
Amortized Cost	1,003,947	1,001,836
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(155,147)	(186,904)
Fair Value	848,800	814,932
U.S. government agency and U.S. government-sponsored enterprise mortgage-backed securities - Commercial mortgage-backed securities
AFS debt securities:
Amortized Cost	482,291	531,377
Gross Unrealized Gains	770	158
Gross Unrealized Losses	(38,184)	(63,276)
Fair Value	444,877	468,259
HTM debt securities:
Amortized Cost	489,133	493,348
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(69,765)	(88,968)
Fair Value	419,368	404,380
U.S. government agency and U.S. government-sponsored enterprise mortgage-backed securities - Residential mortgage-backed securities
AFS debt securities:
Amortized Cost	7,028,428	1,956,927
Gross Unrealized Gains	35,106	380
Gross Unrealized Losses	(195,610)	(229,713)
Fair Value	6,867,924	1,727,594
HTM debt securities:
Amortized Cost	713,634	742,436
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(124,829)	(142,119)
Fair Value	588,805	600,317
Municipal securities
AFS debt securities:
Amortized Cost	292,041	297,283
Gross Unrealized Gains	97	75
Gross Unrealized Losses	(31,840)	(36,342)
Fair Value	260,298	261,016
HTM debt securities:
Amortized Cost	188,002	188,872
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(39,767)	(43,081)
Fair Value	148,235	145,791
Non-agency commercial mortgage-backed securities
AFS debt securities:
Amortized Cost	348,749	409,578
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(32,236)	(42,062)
Fair Value	316,513	367,516
Non-agency residential mortgage-backed securities
AFS debt securities:
Amortized Cost	548,110	643,335
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(68,783)	(89,664)
Fair Value	479,327	553,671
Corporate debt securities
AFS debt securities:
Amortized Cost	653,501	653,501
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(121,682)	(151,076)
Fair Value	531,819	502,425
Foreign government bonds
AFS debt securities:
Amortized Cost	247,907	239,333
Gross Unrealized Gains	1,671	69
Gross Unrealized Losses	(10,709)	(11,528)
Fair Value	238,869	227,874
Asset-backed securities
AFS debt securities:
Amortized Cost	36,195	43,234
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(460)	(934)
Fair Value	35,735	42,300
Collateralized loan obligations (“CLOs”)
AFS debt securities:
Amortized Cost	44,500	617,250
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(6)	(4,389)
Fair Value	$ 44,494	$ 612,861