INVESTMENT SECURITIES - Schedule of Investment Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Investment securities
Available-for-sale:
Amount Outstanding	$ 6,013,517	$ 5,120,963
Amortized cost	5,941,321	5,060,135
Allowance for losses	(25)	(27)
Unrealized Gains	39,660	9,844
Unrealized Losses	(103,020)	(151,021)
Fair Value	5,877,936	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	273	1,745
Unrealized Losses	0	0
Fair Value	9,543	55,501
Available-for-sale, accrued interest excluded	24,500	15,900
Available-for-Sale Securities \| Investment securities
Available-for-sale:
Unamortized Premium/(Discount)	(72,196)	(60,828)
Held-to-maturity:
Unamortized Premium/(Discount)	(72,196)	(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	2,450,408	2,454,009
Amortized cost	2,449,883	2,452,871
Allowance for losses	0	0
Unrealized Gains	3,756	1,212
Unrealized Losses	(17,204)	(29,649)
Fair Value	2,436,435	2,424,434
Floating interest rate \| US Treasuries
Available-for-sale:
Amount Outstanding	0	50,000
Amortized cost	0	49,983
Allowance for losses	0	0
Unrealized Gains	0	0
Unrealized Losses	0	(15)
Fair Value	0	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)	(525)	(1,138)
Held-to-maturity:
Unamortized Premium/(Discount)	(525)	(1,138)
Floating interest rate \| Available-for-Sale Securities \| US Treasuries
Available-for-sale:
Unamortized Premium/(Discount)	0	(17)
Held-to-maturity:
Unamortized Premium/(Discount)	0	(17)
Fixed Interest Rate \| Guaranteed mortgage-backed securities
Available-for-sale:
Amount Outstanding	2,262,332	1,727,669
Amortized cost	2,203,239	1,680,881
Allowance for losses	0	0
Unrealized Gains	25,573	6,558
Unrealized Losses	(85,054)	(117,824)
Fair Value	2,143,758	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	273	1,745
Unrealized Losses	0	0
Fair Value	$ 9,543	$ 55,501
Held-to-maturity investment securities weighted average yield	6.40%	6.70%
Fixed Interest Rate \| US Treasuries
Available-for-sale:
Amount Outstanding	$ 1,281,077	$ 869,585
Amortized cost	1,268,499	856,700
Allowance for losses	0	0
Unrealized Gains	10,331	2,074
Unrealized Losses	(565)	(2,942)
Fair Value	1,278,265	855,832
Fixed Interest Rate \| Available-for-Sale Securities \| Guaranteed mortgage-backed securities
Available-for-sale:
Unamortized Premium/(Discount)	(59,093)	(46,788)
Held-to-maturity:
Unamortized Premium/(Discount)	(59,093)	(46,788)
Fixed Interest Rate \| Available-for-Sale Securities \| US Treasuries
Available-for-sale:
Unamortized Premium/(Discount)	(12,578)	(12,885)
Held-to-maturity:
Unamortized Premium/(Discount)	(12,578)	(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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