INVESTMENT SECURITIES - Unrealized Loss Position (Details) $ in Thousands	Sep. 30, 2024 USD ($) security	Dec. 31, 2023 USD ($) security
Debt Securities, Available-for-sale [Line Items]
Unrealized loss position for less than 12 months, fair value	$ 586,175	$ 1,143,468
Unrealized loss position for less than 12 months, unrealized loss	(908)	(9,278)
Unrealized loss position for more than 12 months, fair value	2,163,973	2,611,155
Unrealized loss position for more than 12 months, unrealized loss	$ (102,112)	$ (141,743)
Investment securities
Debt Securities, Available-for-sale [Line Items]
Unrealized loss position for less than 12 months, number of securities in loss position | security	39	91
Unrealized loss position for more than 12 months, number of securities in loss position | security	148	162
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	19,478	19,082
Unrealized loss position for more than 12 months, unrealized loss	(197)	(591)
Floating interest rate | Guaranteed mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Unrealized loss position for less than 12 months, fair value	367,575	568,759
Unrealized loss position for less than 12 months, unrealized loss	(514)	(4,395)
Unrealized loss position for more than 12 months, fair value	1,074,472	1,449,122
Unrealized loss position for more than 12 months, unrealized loss	(16,690)	(25,254)
Floating interest rate | US Treasuries
Debt Securities, Available-for-sale [Line Items]
Unrealized loss position for less than 12 months, fair value	0	49,969
Unrealized loss position for less than 12 months, unrealized loss	0	(15)
Unrealized loss position for more than 12 months, fair value	0	0
Unrealized loss position for more than 12 months, unrealized loss	0	0
Fixed Interest Rate | Guaranteed mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Unrealized loss position for less than 12 months, fair value	24,873	384,305
Unrealized loss position for less than 12 months, unrealized loss	(42)	(4,262)
Unrealized loss position for more than 12 months, fair value	986,007	905,759
Unrealized loss position for more than 12 months, unrealized loss	(85,012)	(113,562)
Fixed Interest Rate | US Treasuries
Debt Securities, Available-for-sale [Line Items]
Unrealized loss position for less than 12 months, fair value	193,727	140,435
Unrealized loss position for less than 12 months, unrealized loss	(352)	(606)
Unrealized loss position for more than 12 months, fair value	84,016	237,192
Unrealized loss position for more than 12 months, unrealized loss	$ (213)	$ (2,336)