Investment Securities - Schedule of Investment Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Investment securities:
Available-for-sale:
Amount Outstanding	$ 4,607,471	$ 3,819,376
Unamortized Premium/(Discount)	0	0
Amortized cost	4,590,696	3,834,714
Allowance for losses	(38)	(52)
Unrealized Gains	2,679	12,203
Unrealized Losses	(191,458)	(10,474)
Fair Value	4,401,879	3,836,391
Held-to-maturity:
Unamortized Premium/(Discount)	0	0
Amortized Cost	45,032	44,970
Total held-to-maturity
Amount Outstanding	45,032	44,970
Unamortized Premium/(Discount)	0	0
Amortized Cost	45,032	44,970
Allowance for losses	0	0
Unrealized Gains	0	1,612
Unrealized Losses	(1,758)	0
Fair Value	43,274	46,582
Available-for-sale, accrued interest excluded	6,300	4,300
Available-for-Sale Securities \| Investment securities:
Available-for-sale:
Unamortized Premium/(Discount)	(16,775)	15,338
Held-to-maturity:
Unamortized Premium/(Discount)	(16,775)	15,338
Total held-to-maturity
Unamortized Premium/(Discount)	(16,775)	15,338
Floating Interest Rate \| Floating rate auction-rate certificates backed by Government guaranteed student loans
Available-for-sale:
Amount Outstanding	19,700	19,700
Amortized cost	19,700	19,700
Allowance for losses	(38)	(52)
Unrealized Gains	0	0
Unrealized Losses	(419)	(394)
Fair Value	19,243	19,254
Floating Interest Rate \| Guaranteed mortgage-backed securities
Available-for-sale:
Amount Outstanding	2,383,351	2,168,016
Amortized cost	2,383,384	2,168,106
Allowance for losses	0	0
Unrealized Gains	2,679	11,821
Unrealized Losses	(25,535)	(1,096)
Fair Value	2,360,528	2,178,831
Floating Interest Rate \| Available-for-Sale Securities \| Floating rate auction-rate certificates backed by Government guaranteed student loans
Available-for-sale:
Unamortized Premium/(Discount)	0	0
Held-to-maturity:
Unamortized Premium/(Discount)	0	0
Total held-to-maturity
Unamortized Premium/(Discount)	0	0
Floating Interest Rate \| Available-for-Sale Securities \| Guaranteed mortgage-backed securities
Available-for-sale:
Unamortized Premium/(Discount)	33	90
Held-to-maturity:
Unamortized Premium/(Discount)	33	90
Total held-to-maturity
Unamortized Premium/(Discount)	33	90
Fixed Interest Rate \| Guaranteed mortgage-backed securities
Available-for-sale:
Amount Outstanding	993,305	451,660
Amortized cost	980,535	464,185
Allowance for losses	0	0
Unrealized Gains	0	382
Unrealized Losses	(138,831)	(5,730)
Fair Value	841,704	458,837
Held-to-maturity:
Amount Outstanding	45,032	44,970
Amortized Cost	45,032	44,970
Allowance for losses	0	0
Unrealized Gains	0	1,612
Unrealized Losses	(1,758)	0
Fair Value	$ 43,274	$ 46,582
Total held-to-maturity
Held-to-maturity investment securities weighted average yield	3.00%	1.50%
Fixed Interest Rate \| Fixed rate U.S. Treasuries
Available-for-sale:
Amount Outstanding	$ 1,211,115	$ 1,180,000
Amortized cost	1,207,077	1,182,723
Allowance for losses	0	0
Unrealized Gains	0	0
Unrealized Losses	(26,673)	(3,254)
Fair Value	1,180,404	1,179,469
Fixed Interest Rate \| Available-for-Sale Securities \| Guaranteed mortgage-backed securities
Available-for-sale:
Unamortized Premium/(Discount)	(12,770)	12,525
Held-to-maturity:
Unamortized Premium/(Discount)	(12,770)	12,525
Total held-to-maturity
Unamortized Premium/(Discount)	(12,770)	12,525
Fixed Interest Rate \| Available-for-Sale Securities \| Fixed rate U.S. Treasuries
Available-for-sale:
Unamortized Premium/(Discount)	(4,038)	2,723
Held-to-maturity:
Unamortized Premium/(Discount)	(4,038)	2,723
Total held-to-maturity
Unamortized Premium/(Discount)	(4,038)	2,723
Fixed Interest Rate \| Held-to-Maturity Securities \| Guaranteed mortgage-backed securities
Available-for-sale:
Unamortized Premium/(Discount)	0	0
Held-to-maturity:
Unamortized Premium/(Discount)	0	0
Total held-to-maturity
Unamortized Premium/(Discount)	$ 0	$ 0

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