Investment Securities - Schedule of Investment Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Investment securities:
Available-for-sale:
Amount Outstanding	$ 4,358,016	$ 3,819,376
Unamortized Premium/(Discount)	0	0
Amortized cost	4,354,855	3,834,714
Allowance for losses	(48)	(52)
Unrealized Gains	6,834	12,203
Unrealized Losses	(115,629)	(10,474)
Fair Value	4,246,012	3,836,391
Held-to-maturity:
Unamortized Premium/(Discount)	0	0
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	(361)	0
Fair Value	44,671	46,582
Available-for-sale, accrued interest excluded	4,300	4,300
Available-for-Sale Securities \| Investment securities:
Available-for-sale:
Unamortized Premium/(Discount)	(3,161)	15,338
Held-to-maturity:
Unamortized Premium/(Discount)	(3,161)	15,338
Total held-to-maturity
Unamortized Premium/(Discount)	(3,161)	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	(48)	(52)
Unrealized Gains	0	0
Unrealized Losses	(591)	(394)
Fair Value	19,061	19,254
Floating Interest Rate \| Guaranteed mortgage-backed securities
Available-for-sale:
Amount Outstanding	2,379,150	2,168,016
Amortized cost	2,378,934	2,168,106
Allowance for losses	0	0
Unrealized Gains	6,424	11,821
Unrealized Losses	(12,899)	(1,096)
Fair Value	2,372,459	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)	(216)	90
Held-to-maturity:
Unamortized Premium/(Discount)	(216)	90
Total held-to-maturity
Unamortized Premium/(Discount)	(216)	90
Fixed Interest Rate \| Guaranteed mortgage-backed securities
Available-for-sale:
Amount Outstanding	756,951	451,660
Amortized cost	756,354	464,185
Allowance for losses	0	0
Unrealized Gains	410	382
Unrealized Losses	(79,086)	(5,730)
Fair Value	677,678	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	(361)	0
Fair Value	$ 44,671	$ 46,582
Total held-to-maturity
Held-to-maturity investment securities weighted average yield	1.80%	1.50%
Fixed Interest Rate \| Fixed rate U.S. Treasuries
Available-for-sale:
Amount Outstanding	$ 1,202,215	$ 1,180,000
Amortized cost	1,199,867	1,182,723
Allowance for losses	0	0
Unrealized Gains	0	0
Unrealized Losses	(23,053)	(3,254)
Fair Value	1,176,814	1,179,469
Fixed Interest Rate \| Available-for-Sale Securities \| Guaranteed mortgage-backed securities
Available-for-sale:
Unamortized Premium/(Discount)	(597)	12,525
Held-to-maturity:
Unamortized Premium/(Discount)	(597)	12,525
Total held-to-maturity
Unamortized Premium/(Discount)	(597)	12,525
Fixed Interest Rate \| Available-for-Sale Securities \| Fixed rate U.S. Treasuries
Available-for-sale:
Unamortized Premium/(Discount)	(2,348)	2,723
Held-to-maturity:
Unamortized Premium/(Discount)	(2,348)	2,723
Total held-to-maturity
Unamortized Premium/(Discount)	(2,348)	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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