INVESTMENT SECURITIES - Schedule of Investment Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Investment Securities
Available-for-sale:
Amount Outstanding	$ 5,483,836	$ 5,120,963
Amortized cost	5,410,032	5,060,135
Allowance for losses	(25)	(27)
Unrealized Gains	5,788	9,844
Unrealized Losses	(167,080)	(151,021)
Fair Value	5,248,715	4,918,931
Held-to-maturity:
Amount Outstanding	9,270	53,756
Amortized cost	9,270	53,756
Allowance for losses	0	0
Unrealized Gains	226	1,745
Unrealized Losses	0	0
Fair Value	9,496	55,501
Available-for-sale, accrued interest excluded	19,400	15,900
Available-for-Sale Securities \| Investment Securities
Available-for-sale:
Unamortized Premium/(Discount)	(73,804)	(60,828)
Held-to-maturity:
Unamortized Premium/(Discount)	(73,804)	(60,828)
Held-to-Maturity Securities \| Investment Securities
Available-for-sale:
Unamortized Premium/(Discount)	0	0
Held-to-maturity:
Unamortized Premium/(Discount)	0	0
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	(25)	(27)
Unrealized Gains	0	0
Unrealized Losses	(197)	(591)
Fair Value	19,478	19,082
Floating interest rate \| Guaranteed mortgage-backed securities
Available-for-sale:
Amount Outstanding	2,262,092	2,454,009
Amortized cost	2,262,121	2,452,871
Allowance for losses	0	0
Unrealized Gains	3,037	1,212
Unrealized Losses	(20,258)	(29,649)
Fair Value	2,244,900	2,424,434
Floating interest rate \| US Treasuries
Available-for-sale:
Amount Outstanding	50,000	50,000
Amortized cost	49,996	49,983
Allowance for losses	0	0
Unrealized Gains	0	0
Unrealized Losses	(6)	(15)
Fair Value	49,990	49,968
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
Floating interest rate \| Available-for-Sale Securities \| Guaranteed mortgage-backed securities
Available-for-sale:
Unamortized Premium/(Discount)	29	(1,138)
Held-to-maturity:
Unamortized Premium/(Discount)	29	(1,138)
Floating interest rate \| Available-for-Sale Securities \| US Treasuries
Available-for-sale:
Unamortized Premium/(Discount)	(4)	(17)
Held-to-maturity:
Unamortized Premium/(Discount)	(4)	(17)
Fixed Interest Rate \| Guaranteed mortgage-backed securities
Available-for-sale:
Amount Outstanding	2,111,417	1,727,669
Amortized cost	2,052,743	1,680,881
Allowance for losses	0	0
Unrealized Gains	2,584	6,558
Unrealized Losses	(141,565)	(117,824)
Fair Value	1,913,762	1,569,615
Held-to-maturity:
Amount Outstanding	9,270	53,756
Amortized cost	9,270	53,756
Allowance for losses	0	0
Unrealized Gains	226	1,745
Unrealized Losses	0	0
Fair Value	$ 9,496	$ 55,501
Held-to-maturity investment securities weighted average yield	6.40%	6.70%
Fixed Interest Rate \| US Treasuries
Available-for-sale:
Amount Outstanding	$ 1,040,627	$ 869,585
Amortized cost	1,025,472	856,700
Allowance for losses	0	0
Unrealized Gains	167	2,074
Unrealized Losses	(5,054)	(2,942)
Fair Value	1,020,585	855,832
Fixed Interest Rate \| Available-for-Sale Securities \| Guaranteed mortgage-backed securities
Available-for-sale:
Unamortized Premium/(Discount)	(58,674)	(46,788)
Held-to-maturity:
Unamortized Premium/(Discount)	(58,674)	(46,788)
Fixed Interest Rate \| Available-for-Sale Securities \| US Treasuries
Available-for-sale:
Unamortized Premium/(Discount)	(15,155)	(12,885)
Held-to-maturity:
Unamortized Premium/(Discount)	(15,155)	(12,885)
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

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