Securities - Scheduled Contractual Maturities of ATM and HTM Debt Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Amortized cost
Within One Year	$ 618,788
After One Year through Five Years	1,032,511
After Five Years through Ten Years	998,302
After Ten Years	4,266,890
Amortized Cost	6,916,491	$ 6,879,225
Fair value
Within One Year	617,580
After One Year through Five Years	970,877
After Five Years through Ten Years	904,294
After Ten Years	3,695,586
Total	$ 6,188,337
Weighted-Average Yield
Within One Year	5.44%
After One Year through Five Years	1.84%
After Five Years through Ten Years	4.27%
After Ten Years	3.42%
Total	3.49%
Amortized cost
Within One Year	$ 0
After One Year through Five Years	529,548
After Five Years through Ten Years	442,792
After Ten Years	1,983,700
Total	2,956,040
Fair value
Within One Year	0
After One Year through Five Years	488,551
After Five Years through Ten Years	380,447
After Ten Years	1,584,973
Total	$ 2,453,971
Weighted Average Yield
Within One Year	0.00%
After One Year through Five Years	1.05%
After Five Years through Ten Years	1.83%
After Ten Years	1.79%
Total	1.66%
U.S. Treasury securities
Amortized cost
Within One Year	$ 436,296
After One Year through Five Years	676,291
After Five Years through Ten Years	0
After Ten Years	0
Amortized Cost	1,112,587	676,306
Fair value
Within One Year	436,397
After One Year through Five Years	623,978
After Five Years through Ten Years	0
After Ten Years	0
Total	$ 1,060,375
Weighted-Average Yield
Within One Year	5.40%
After One Year through Five Years	1.20%
After Five Years through Ten Years	0.00%
After Ten Years	0.00%
Total	2.85%
Amortized cost
Within One Year	$ 0
After One Year through Five Years	529,548
After Five Years through Ten Years	0
After Ten Years	0
Total	529,548
Fair value
Within One Year	0
After One Year through Five Years	488,551
After Five Years through Ten Years	0
After Ten Years	0
Total	$ 488,551
Weighted Average Yield
Within One Year	0.00%
After One Year through Five Years	1.05%
After Five Years through Ten Years	0.00%
After Ten Years	0.00%
Total	1.05%
U.S. government agency and U.S. government-sponsored enterprise debt securities
Amortized cost
Within One Year	$ 50,000
After One Year through Five Years	96,470
After Five Years through Ten Years	128,169
After Ten Years	137,447
Amortized Cost	412,086	517,806
Fair value
Within One Year	49,882
After One Year through Five Years	93,182
After Five Years through Ten Years	109,134
After Ten Years	112,248
Total	$ 364,446
Weighted-Average Yield
Within One Year	5.00%
After One Year through Five Years	3.08%
After Five Years through Ten Years	1.38%
After Ten Years	2.33%
Total	2.53%
Amortized cost
Within One Year	$ 0
After One Year through Five Years	0
After Five Years through Ten Years	343,319
After Ten Years	658,517
Total	1,001,836
Fair value
Within One Year	0
After One Year through Five Years	0
After Five Years through Ten Years	296,124
After Ten Years	518,808
Total	$ 814,932
Weighted Average Yield
Within One Year	0.00%
After One Year through Five Years	0.00%
After Five Years through Ten Years	1.90%
After Ten Years	1.89%
Total	1.90%
U.S. government agency and U.S. government-sponsored enterprise mortgage-backed securities
Amortized cost
Within One Year	$ 0
After One Year through Five Years	41,533
After Five Years through Ten Years	142,008
After Ten Years	2,304,763
Amortized Cost	2,488,304
Fair value
Within One Year	0
After One Year through Five Years	39,930
After Five Years through Ten Years	130,528
After Ten Years	2,025,395
Total	$ 2,195,853
Weighted-Average Yield
Within One Year	0.00%
After One Year through Five Years	3.13%
After Five Years through Ten Years	2.70%
After Ten Years	3.68%
Total	3.62%
Amortized cost
Within One Year	$ 0
After One Year through Five Years	0
After Five Years through Ten Years	99,473
After Ten Years	1,136,311
Total	1,235,784
Fair value
Within One Year	0
After One Year through Five Years	0
After Five Years through Ten Years	84,323
After Ten Years	920,374
Total	$ 1,004,697
Weighted Average Yield
Within One Year	0.00%
After One Year through Five Years	0.00%
After Five Years through Ten Years	1.61%
After Ten Years	1.70%
Total	1.69%
Municipal securities:
Amortized cost
Within One Year	$ 2,240
After One Year through Five Years	35,100
After Five Years through Ten Years	9,624
After Ten Years	250,319
Amortized Cost	297,283	303,884
Fair value
Within One Year	2,214
After One Year through Five Years	32,877
After Five Years through Ten Years	8,752
After Ten Years	217,173
Total	$ 261,016
Weighted-Average Yield
Within One Year	3.39%
After One Year through Five Years	2.24%
After Five Years through Ten Years	3.22%
After Ten Years	2.23%
Total	2.27%
Amortized cost
Within One Year	$ 0
After One Year through Five Years	0
After Five Years through Ten Years	0
After Ten Years	188,872
Total	188,872
Fair value
Within One Year	0
After One Year through Five Years	0
After Five Years through Ten Years	0
After Ten Years	145,791
Total	$ 145,791
Weighted Average Yield
Within One Year	0.00%
After One Year through Five Years	0.00%
After Five Years through Ten Years	0.00%
After Ten Years	1.99%
Total	1.99%
Non-agency mortgage-backed securities
Amortized cost
Within One Year	$ 96,990
After One Year through Five Years	77,046
After Five Years through Ten Years	0
After Ten Years	878,877
Amortized Cost	1,052,913
Fair value
Within One Year	95,856
After One Year through Five Years	74,884
After Five Years through Ten Years	0
After Ten Years	750,447
Total	$ 921,187
Weighted-Average Yield
Within One Year	6.74%
After One Year through Five Years	4.44%
After Five Years through Ten Years	0.00%
After Ten Years	2.59%
Total	3.11%
Corporate debt securities
Amortized cost
Within One Year	$ 0
After One Year through Five Years	0
After Five Years through Ten Years	349,501
After Ten Years	304,000
Amortized Cost	653,501	673,502
Fair value
Within One Year	0
After One Year through Five Years	0
After Five Years through Ten Years	290,877
After Ten Years	211,548
Total	$ 502,425
Weighted-Average Yield
Within One Year	0.00%
After One Year through Five Years	0.00%
After Five Years through Ten Years	3.48%
After Ten Years	1.97%
Total	2.78%
Foreign government bonds
Amortized cost
Within One Year	$ 33,262
After One Year through Five Years	106,071
After Five Years through Ten Years	50,000
After Ten Years	50,000
Amortized Cost	239,333	241,165
Fair value
Within One Year	33,231
After One Year through Five Years	106,026
After Five Years through Ten Years	49,593
After Ten Years	39,024
Total	$ 227,874
Weighted-Average Yield
Within One Year	3.02%
After One Year through Five Years	2.28%
After Five Years through Ten Years	5.73%
After Ten Years	1.50%
Total	2.94%
Asset-backed securities
Amortized cost
Within One Year	$ 0
After One Year through Five Years	0
After Five Years through Ten Years	0
After Ten Years	43,234
Amortized Cost	43,234	51,152
Fair value
Within One Year	0
After One Year through Five Years	0
After Five Years through Ten Years	0
After Ten Years	42,300
Total	$ 42,300
Weighted-Average Yield
Within One Year	0.00%
After One Year through Five Years	0.00%
After Five Years through Ten Years	0.00%
After Ten Years	6.07%
Total	6.07%
Collateralized loan obligations (“CLOs”)
Amortized cost
Within One Year	$ 0
After One Year through Five Years	0
After Five Years through Ten Years	319,000
After Ten Years	298,250
Amortized Cost	617,250	$ 617,250
Fair value
Within One Year	0
After One Year through Five Years	0
After Five Years through Ten Years	315,410
After Ten Years	297,451
Total	$ 612,861
Weighted-Average Yield
Within One Year	0.00%
After One Year through Five Years	0.00%
After Five Years through Ten Years	6.80%
After Ten Years	6.82%
Total	6.81%