INVESTMENT SECURITIES - Schedule of Investment Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Dec. 31, 2024
Investment securities
Available-for-sale:
Amount Outstanding	$ 6,790,794	$ 6,183,545
Amortized Cost	6,714,777	6,105,116
Allowance for losses	(21)	(27)
Unrealized Gains	36,672	9,514
Unrealized Losses	(95,482)	(161,589)
Fair Value	6,655,946	5,953,014
Held-to-maturity:
Amount Outstanding	8,815	9,270
Amortized cost	8,815	9,270
Allowance for losses	0	0
Unrealized Gains	286	270
Unrealized Losses	0	0
Fair Value	9,101	9,540
Available-for-sale, accrued interest excluded	30,900	22,300
Available-for-Sale Securities \| Investment securities
Available-for-sale:
Unamortized Premium/(Discount)	(76,017)	(78,429)
Held-to-maturity:
Unamortized Premium/(Discount)	(76,017)	(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	(21)	(27)
Unrealized Gains	0	0
Unrealized Losses	(197)	(197)
Fair Value	19,482	19,476
Floating interest rate \| Guaranteed mortgage-backed securities
Available-for-sale:
Amount Outstanding	2,326,063	2,317,032
Amortized Cost	2,324,640	2,316,191
Allowance for losses	0	0
Unrealized Gains	1,669	3,484
Unrealized Losses	(12,459)	(13,950)
Fair Value	2,313,850	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)	(1,423)	(841)
Held-to-maturity:
Unamortized Premium/(Discount)	(1,423)	(841)
Fixed Interest Rate \| Guaranteed mortgage-backed securities
Available-for-sale:
Amount Outstanding	2,967,739	2,544,136
Amortized Cost	2,899,644	2,477,291
Allowance for losses	0	0
Unrealized Gains	28,975	3,426
Unrealized Losses	(82,498)	(142,750)
Fair Value	2,846,121	2,337,967
Held-to-maturity:
Amount Outstanding	8,815	9,270
Amortized cost	8,815	9,270
Allowance for losses	0	0
Unrealized Gains	286	270
Unrealized Losses	0	0
Fair Value	$ 9,101	$ 9,540
Held-to-maturity investment securities weighted average yield	6.40%	6.40%
Fixed Interest Rate \| Fixed rate U.S. Treasuries
Available-for-sale:
Amount Outstanding	$ 1,477,292	$ 1,302,677
Amortized Cost	1,470,793	1,291,934
Allowance for losses	0	0
Unrealized Gains	6,028	2,604
Unrealized Losses	(328)	(4,692)
Fair Value	1,476,493	1,289,846
Fixed Interest Rate \| Available-for-Sale Securities \| Guaranteed mortgage-backed securities
Available-for-sale:
Unamortized Premium/(Discount)	(68,095)	(66,845)
Held-to-maturity:
Unamortized Premium/(Discount)	(68,095)	(66,845)
Fixed Interest Rate \| Available-for-Sale Securities \| Fixed rate U.S. Treasuries
Available-for-sale:
Unamortized Premium/(Discount)	(6,499)	(10,743)
Held-to-maturity:
Unamortized Premium/(Discount)	(6,499)	(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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