Securities - Schedule of Debt Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
AFS debt securities:
Amortized Cost	$ 9,131,953	$ 6,916,491
Gross Unrealized Gains	4,993	783
Gross Unrealized Losses	(736,478)	(728,937)
Fair Value	8,400,468	6,188,337
HTM debt securities:
Amortized Cost	2,948,642	2,956,040
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(534,164)	(502,069)
Fair Value	2,414,478	2,453,971
Total debt securities
Amortized Cost	12,080,595	9,872,531
Gross Unrealized Gains	4,993	783
Gross Unrealized Losses	(1,270,642)	(1,231,006)
Fair Value	10,814,946	8,642,308
AFS and HTM, accrued interest	40,000	44,000
Government National Mortgage Association (GNMA)
AFS debt securities:
Amortized Cost	4,500,000	1,300,000
Fair Value	4,400,000	1,200,000
HTM debt securities:
Amortized Cost	91,000	92,000
Fair Value	73,000	75,000
U.S. Treasury securities
AFS debt securities:
Amortized Cost	676,290	1,112,587
Gross Unrealized Gains	0	101
Gross Unrealized Losses	(55,196)	(52,313)
Fair Value	621,094	1,060,375
HTM debt securities:
Amortized Cost	530,921	529,548
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(45,521)	(40,997)
Fair Value	485,400	488,551
U.S. government agency and U.S. government-sponsored enterprise debt securities
AFS debt securities:
Amortized Cost	410,676	412,086
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(49,874)	(47,640)
Fair Value	360,802	364,446
HTM debt securities:
Amortized Cost	1,002,697	1,001,836
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(196,898)	(186,904)
Fair Value	805,799	814,932
U.S. government agency and U.S. government-sponsored enterprise mortgage-backed securities - Commercial mortgage-backed securities
AFS debt securities:
Amortized Cost	513,159	531,377
Gross Unrealized Gains	129	158
Gross Unrealized Losses	(57,669)	(63,276)
Fair Value	455,619	468,259
HTM debt securities:
Amortized Cost	491,842	493,348
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(93,850)	(88,968)
Fair Value	397,992	404,380
U.S. government agency and U.S. government-sponsored enterprise mortgage-backed securities - Residential mortgage-backed securities
AFS debt securities:
Amortized Cost	5,229,549	1,956,927
Gross Unrealized Gains	4,212	380
Gross Unrealized Losses	(241,362)	(229,713)
Fair Value	4,992,399	1,727,594
HTM debt securities:
Amortized Cost	734,577	742,436
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(153,299)	(142,119)
Fair Value	581,278	600,317
Municipal securities
AFS debt securities:
Amortized Cost	296,360	297,283
Gross Unrealized Gains	47	75
Gross Unrealized Losses	(37,912)	(36,342)
Fair Value	258,495	261,016
HTM debt securities:
Amortized Cost	188,605	188,872
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(44,596)	(43,081)
Fair Value	144,009	145,791
Non-agency commercial mortgage-backed securities
AFS debt securities:
Amortized Cost	373,834	409,578
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(39,838)	(42,062)
Fair Value	333,996	367,516
Non-agency residential mortgage-backed securities
AFS debt securities:
Amortized Cost	609,705	643,335
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(90,048)	(89,664)
Fair Value	519,657	553,671
Corporate debt securities
AFS debt securities:
Amortized Cost	653,501	653,501
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(150,854)	(151,076)
Fair Value	502,647	502,425
Foreign government bonds
AFS debt securities:
Amortized Cost	238,592	239,333
Gross Unrealized Gains	605	69
Gross Unrealized Losses	(12,001)	(11,528)
Fair Value	227,196	227,874
Asset-backed securities
AFS debt securities:
Amortized Cost	41,287	43,234
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(575)	(934)
Fair Value	40,712	42,300
Collateralized loan obligations (“CLOs”)
AFS debt securities:
Amortized Cost	89,000	617,250
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1,149)	(4,389)
Fair Value	$ 87,851	$ 612,861