INVESTMENT SECURITIES - Schedule of Investment Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Investment securities
Available-for-sale:
Amount Outstanding	$ 5,120,963	$ 4,806,727
Unamortized Premium/(Discount)	0	0
Amortized cost	5,060,135	4,769,426
Allowance for losses	(27)	(33)
Unrealized Gains	9,844	4,703
Unrealized Losses	(151,021)	(194,532)
Fair Value	4,918,931	4,579,564
Held-to-maturity:
Amount Outstanding	53,756	45,032
Unamortized Premium/(Discount)	0	0
Amortized Cost	53,756	45,032
Allowance for losses	0	0
Unrealized Gains	1,745	2,433
Unrealized Losses	0	0
Fair Value	55,501	47,465
Available-for-sale, accrued interest excluded	15,900	10,600
Available-for-Sale Securities \| Investment securities
Available-for-sale:
Unamortized Premium/(Discount)	(60,828)	(37,301)
Held-to-maturity:
Unamortized Premium/(Discount)	(60,828)	(37,301)
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	(27)	(33)
Unrealized Gains	0	0
Unrealized Losses	(591)	(640)
Fair Value	19,082	19,027
Floating interest rate \| Guaranteed mortgage-backed securities
Available-for-sale:
Amount Outstanding	2,454,009	2,433,696
Amortized cost	2,452,871	2,433,496
Allowance for losses	0	0
Unrealized Gains	1,212	1,954
Unrealized Losses	(29,649)	(42,910)
Fair Value	2,424,434	2,392,540
Floating interest rate \| Fixed rate U.S. Treasuries
Available-for-sale:
Amount Outstanding	50,000
Amortized cost	49,983
Allowance for losses	0
Unrealized Gains	0
Unrealized Losses	(15)
Fair Value	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)	(1,138)	(200)
Held-to-maturity:
Unamortized Premium/(Discount)	(1,138)	(200)
Floating interest rate \| Available-for-Sale Securities \| Fixed rate U.S. Treasuries
Available-for-sale:
Unamortized Premium/(Discount)	(17)
Held-to-maturity:
Unamortized Premium/(Discount)	(17)
Fixed Interest Rate \| Guaranteed mortgage-backed securities
Available-for-sale:
Amount Outstanding	1,727,669	1,207,416
Amortized cost	1,680,881	1,177,095
Allowance for losses	0	0
Unrealized Gains	6,558	2,128
Unrealized Losses	(117,824)	(130,837)
Fair Value	1,569,615	1,048,386
Held-to-maturity:
Amount Outstanding	53,756	45,032
Amortized Cost	53,756	45,032
Allowance for losses	0	0
Unrealized Gains	1,745	2,433
Unrealized Losses	0	0
Fair Value	$ 55,501	$ 47,465
Held-to-maturity investment securities weighted average yield	6.70%	4.50%
Fixed Interest Rate \| Fixed rate U.S. Treasuries
Available-for-sale:
Amount Outstanding	$ 869,585	$ 1,145,915
Amortized cost	856,700	1,139,135
Allowance for losses	0	0
Unrealized Gains	2,074	621
Unrealized Losses	(2,942)	(20,145)
Fair Value	855,832	1,119,611
Fixed Interest Rate \| Available-for-Sale Securities \| Guaranteed mortgage-backed securities
Available-for-sale:
Unamortized Premium/(Discount)	(46,788)	(30,321)
Held-to-maturity:
Unamortized Premium/(Discount)	(46,788)	(30,321)
Fixed Interest Rate \| Available-for-Sale Securities \| Fixed rate U.S. Treasuries
Available-for-sale:
Unamortized Premium/(Discount)	(12,885)	(6,780)
Held-to-maturity:
Unamortized Premium/(Discount)	(12,885)	(6,780)
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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