Securities - Schedule of Debt Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
AFS debt securities:
Amortized Cost	$ 6,976,331	$ 6,879,225
Gross Unrealized Gains	138	498
Gross Unrealized Losses	(936,632)	(844,730)
Fair Value	6,039,837	6,034,993
HTM debt securities:
Amortized Cost	2,964,235	3,001,868
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(656,187)	(546,697)
Fair Value	2,308,048	2,455,171
Total debt securities
Amortized Cost	9,940,566	9,881,093
Gross Unrealized Gains	138	498
Gross Unrealized Losses	(1,592,819)	(1,391,427)
Fair Value	8,347,885	8,490,164
U.S. Treasury securities
AFS debt securities:
Amortized Cost	974,615	676,306
Gross Unrealized Gains	48	0
Gross Unrealized Losses	(70,562)	(70,103)
Fair Value	904,101	606,203
HTM debt securities:
Amortized Cost	528,169	524,081
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(57,551)	(52,612)
Fair Value	470,618	471,469
U.S. government agency and U.S. government-sponsored enterprise debt securities
AFS debt securities:
Amortized Cost	512,712	517,806
Gross Unrealized Gains	0	67
Gross Unrealized Losses	(65,248)	(56,266)
Fair Value	447,464	461,607
HTM debt securities:
Amortized Cost	1,001,298	998,972
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(249,007)	(209,560)
Fair Value	752,291	789,412
U.S. government agency and U.S. government-sponsored enterprise mortgage-backed securities - Commercial mortgage-backed securities
AFS debt securities:
Amortized Cost	545,086	577,392
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(82,754)	(77,123)
Fair Value	462,332	500,269
HTM debt securities:
Amortized Cost	494,787	506,965
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(112,623)	(98,566)
Fair Value	382,164	408,399
U.S. government agency and U.S. government-sponsored enterprise mortgage-backed securities - Residential mortgage-backed securities
AFS debt securities:
Amortized Cost	1,983,284	2,011,054
Gross Unrealized Gains	15	41
Gross Unrealized Losses	(288,957)	(248,900)
Fair Value	1,694,342	1,762,195
HTM debt securities:
Amortized Cost	750,888	782,141
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(183,488)	(148,230)
Fair Value	567,400	633,911
Municipal securities
AFS debt securities:
Amortized Cost	301,408	303,884
Gross Unrealized Gains	0	3
Gross Unrealized Losses	(57,852)	(46,788)
Fair Value	243,556	257,099
HTM debt securities:
Amortized Cost	189,093	189,709
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(53,518)	(37,729)
Fair Value	135,575	151,980
Non-agency commercial mortgage-backed securities
AFS debt securities:
Amortized Cost	418,451	447,512
Gross Unrealized Gains	0	213
Gross Unrealized Losses	(53,131)	(49,396)
Fair Value	365,320	398,329
Non-agency residential mortgage-backed securities
AFS debt securities:
Amortized Cost	687,674	762,202
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(116,887)	(112,978)
Fair Value	570,787	649,224
Corporate debt securities
AFS debt securities:
Amortized Cost	653,501	673,502
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(178,067)	(147,228)
Fair Value	475,434	526,274
Foreign government bonds
AFS debt securities:
Amortized Cost	237,531	241,165
Gross Unrealized Gains	75	174
Gross Unrealized Losses	(14,816)	(14,286)
Fair Value	222,790	227,053
Asset-backed securities
AFS debt securities:
Amortized Cost	44,819	51,152
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1,062)	(2,076)
Fair Value	43,757	49,076
Collateralized loan obligations (“CLOs”)
AFS debt securities:
Amortized Cost	617,250	617,250
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(7,296)	(19,586)
Fair Value	$ 609,954	$ 597,664