Securities - Scheduled Contractual Maturities of AFS (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Amortized cost
Within One Year	$ 583,428
After One Year through Five Years	1,048,858
After Five Years through Ten Years	986,581
After Ten Years	4,357,464
Amortized Cost	6,976,331	$ 6,879,225
Fair value
Within One Year	581,600
After One Year through Five Years	964,501
After Five Years through Ten Years	874,214
After Ten Years	3,619,522
Total	$ 6,039,837
Weighted Average Yield
Within One Year	5.32%
After One Year through Five Years	1.86%
After Five Years through Ten Years	4.27%
After Ten Years	3.40%
Total	3.45%
U.S. Treasury securities
Amortized cost
Within One Year	$ 298,323
After One Year through Five Years	676,292
After Five Years through Ten Years	0
After Ten Years	0
Amortized Cost	974,615
Fair value
Within One Year	298,371
After One Year through Five Years	605,730
After Five Years through Ten Years	0
After Ten Years	0
Total	$ 904,101
Weighted Average Yield
Within One Year	5.44%
After One Year through Five Years	1.20%
After Five Years through Ten Years	0.00%
After Ten Years	0.00%
Total	2.50%
U.S. government-sponsored enterprises debt securities
Amortized cost
Within One Year	$ 150,000
After One Year through Five Years	96,472
After Five Years through Ten Years	103,171
After Ten Years	163,069
Amortized Cost	512,712
Fair value
Within One Year	149,616
After One Year through Five Years	91,343
After Five Years through Ten Years	82,252
After Ten Years	124,253
Total	$ 447,464
Weighted Average Yield
Within One Year	4.98%
After One Year through Five Years	3.08%
After Five Years through Ten Years	1.39%
After Ten Years	2.18%
Total	3.01%
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	42,260
After Five Years through Ten Years	144,846
After Ten Years	2,341,264
Amortized Cost	2,528,370
Fair value
Within One Year	0
After One Year through Five Years	39,718
After Five Years through Ten Years	128,933
After Ten Years	1,988,023
Total	$ 2,156,674
Weighted Average Yield
Within One Year	0.00%
After One Year through Five Years	3.16%
After Five Years through Ten Years	2.73%
After Ten Years	3.68%
Total	3.62%
Municipal securities
Amortized cost
Within One Year	$ 2,400
After One Year through Five Years	36,850
After Five Years through Ten Years	9,007
After Ten Years	253,151
Amortized Cost	301,408
Fair value
Within One Year	2,383
After One Year through Five Years	33,794
After Five Years through Ten Years	7,596
After Ten Years	199,783
Total	$ 243,556
Weighted Average Yield
Within One Year	3.13%
After One Year through Five Years	2.34%
After Five Years through Ten Years	2.87%
After Ten Years	2.24%
Total	2.28%
Non-agency mortgage-backed securities
Amortized cost
Within One Year	$ 99,830
After One Year through Five Years	92,328
After Five Years through Ten Years	11,056
After Ten Years	902,911
Amortized Cost	1,106,125
Fair value
Within One Year	98,420
After One Year through Five Years	89,370
After Five Years through Ten Years	10,793
After Ten Years	737,524
Total	$ 936,107
Weighted Average Yield
Within One Year	6.27%
After One Year through Five Years	4.16%
After Five Years through Ten Years	0.80%
After Ten Years	2.58%
Total	3.02%
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
Fair value
Within One Year	0
After One Year through Five Years	0
After Five Years through Ten Years	280,812
After Ten Years	194,622
Total	$ 475,434
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	$ 32,875
After One Year through Five Years	104,656
After Five Years through Ten Years	50,000
After Ten Years	50,000
Amortized Cost	237,531
Fair value
Within One Year	32,810
After One Year through Five Years	104,546
After Five Years through Ten Years	49,609
After Ten Years	35,825
Total	$ 222,790
Weighted Average Yield
Within One Year	3.02%
After One Year through Five Years	2.28%
After Five Years through Ten Years	5.71%
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	44,819
Amortized Cost	44,819
Fair value
Within One Year	0
After One Year through Five Years	0
After Five Years through Ten Years	0
After Ten Years	43,757
Total	$ 43,757
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	6.01%
Total	6.01%
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
Fair value
Within One Year	0
After One Year through Five Years	0
After Five Years through Ten Years	314,219
After Ten Years	295,735
Total	$ 609,954
Weighted Average Yield
Within One Year	0.00%
After One Year through Five Years	0.00%
After Five Years through Ten Years	6.71%
After Ten Years	6.76%
Total	6.73%