INVESTMENT SECURITIES - Schedule of Investment Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024
Investment securities
Available-for-sale:
Amount Outstanding	$ 6,405,423	$ 6,183,545
Amortized cost	6,329,188	6,105,116
Allowance for losses	(27)	(27)
Unrealized Gains	23,361	9,514
Unrealized Losses	(122,442)	(161,589)
Fair Value	6,230,080	5,953,014
Held-to-maturity:
Amount Outstanding	9,125	9,270
Amortized cost	9,125	9,270
Allowance for losses	0	0
Unrealized Gains	309	270
Unrealized Losses	0	0
Fair Value	9,434	9,540
Available-for-sale, accrued interest excluded	27,100	22,300
Available-for-Sale Securities \| Investment securities
Available-for-sale:
Unamortized Premium/(Discount)	(76,235)	(78,429)
Held-to-maturity:
Unamortized Premium/(Discount)	(76,235)	(78,429)
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	(27)	(27)
Unrealized Gains	0	0
Unrealized Losses	(320)	(197)
Fair Value	19,353	19,476
Floating interest rate \| Guaranteed mortgage-backed securities
Available-for-sale:
Amount Outstanding	2,404,113	2,317,032
Amortized cost	2,402,939	2,316,191
Allowance for losses	0	0
Unrealized Gains	3,046	3,484
Unrealized Losses	(13,888)	(13,950)
Fair Value	2,392,097	2,305,725
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)	(1,174)	(841)
Held-to-maturity:
Unamortized Premium/(Discount)	(1,174)	(841)
Fixed Interest Rate \| Guaranteed mortgage-backed securities
Available-for-sale:
Amount Outstanding	2,661,093	2,544,136
Amortized cost	2,595,137	2,477,291
Allowance for losses	0	0
Unrealized Gains	15,589	3,426
Unrealized Losses	(106,814)	(142,750)
Fair Value	2,503,912	2,337,967
Held-to-maturity:
Amount Outstanding	9,125	9,270
Amortized cost	9,125	9,270
Allowance for losses	0	0
Unrealized Gains	309	270
Unrealized Losses	0	0
Fair Value	$ 9,434	$ 9,540
Held-to-maturity investment securities weighted average yield	6.40%	6.40%
Fixed Interest Rate \| US treasuries
Available-for-sale:
Amount Outstanding	$ 1,320,517	$ 1,302,677
Amortized cost	1,311,412	1,291,934
Allowance for losses	0	0
Unrealized Gains	4,726	2,604
Unrealized Losses	(1,420)	(4,692)
Fair Value	1,314,718	1,289,846
Fixed Interest Rate \| Available-for-Sale Securities \| Guaranteed mortgage-backed securities
Available-for-sale:
Unamortized Premium/(Discount)	(65,956)	(66,845)
Held-to-maturity:
Unamortized Premium/(Discount)	(65,956)	(66,845)
Fixed Interest Rate \| Available-for-Sale Securities \| US treasuries
Available-for-sale:
Unamortized Premium/(Discount)	(9,105)	(10,743)
Held-to-maturity:
Unamortized Premium/(Discount)	(9,105)	(10,743)
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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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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