INVESTMENT SECURITIES - Unrealized Loss Position (Details) $ in Thousands	Jun. 30, 2025 USD ($) security	Dec. 31, 2024 USD ($) security
Debt Securities, Available-for-sale [Line Items]
Unrealized loss position for less than 12 months, fair value	$ 1,383,826	$ 1,859,962
Unrealized loss position for less than 12 months, unrealized loss	(8,760)	(22,477)
Unrealized loss position for more than 12 months, fair value	1,999,182	2,049,525
Unrealized loss position for more than 12 months, unrealized loss	$ (102,362)	$ (139,112)
Investment securities
Debt Securities, Available-for-sale [Line Items]
Unrealized loss position for less than 12 months, number of securities in loss position | security	74	90
Unrealized loss position for more than 12 months, number of securities in loss position | security	156	155
Floating interest rate | Floating rate auction-rate certificates backed by Government guaranteed student loans
Debt Securities, Available-for-sale [Line Items]
Unrealized loss position for less than 12 months, fair value	$ 0	$ 0
Unrealized loss position for less than 12 months, unrealized loss	0	0
Unrealized loss position for more than 12 months, fair value	19,475	19,476
Unrealized loss position for more than 12 months, unrealized loss	(197)	(197)
Floating interest rate | Guaranteed mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Unrealized loss position for less than 12 months, fair value	599,742	269,862
Unrealized loss position for less than 12 months, unrealized loss	(1,272)	(420)
Unrealized loss position for more than 12 months, fair value	976,207	1,025,360
Unrealized loss position for more than 12 months, unrealized loss	(13,761)	(13,530)
Fixed Interest Rate | Guaranteed mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Unrealized loss position for less than 12 months, fair value	399,530	999,793
Unrealized loss position for less than 12 months, unrealized loss	(6,557)	(17,682)
Unrealized loss position for more than 12 months, fair value	964,601	946,166
Unrealized loss position for more than 12 months, unrealized loss	(88,279)	(125,068)
Fixed Interest Rate | Fixed rate U.S. Treasuries
Debt Securities, Available-for-sale [Line Items]
Unrealized loss position for less than 12 months, fair value	384,554	590,307
Unrealized loss position for less than 12 months, unrealized loss	(931)	(4,375)
Unrealized loss position for more than 12 months, fair value	38,899	58,523
Unrealized loss position for more than 12 months, unrealized loss	$ (125)	$ (317)