INVESTMENT SECURITIES - Unrealized Loss Position (Details) $ in Thousands	Mar. 31, 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	$ 1,277,370	$ 1,859,962
Unrealized loss position for less than 12 months, unrealized loss	(9,183)	(22,477)
Unrealized loss position for more than 12 months, fair value	2,051,437	2,049,525
Unrealized loss position for more than 12 months, unrealized loss	$ (113,259)	$ (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	64	90
Unrealized loss position for more than 12 months, number of securities in loss position | security	157	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	19,353	19,476
Unrealized loss position for more than 12 months, unrealized loss	(320)	(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	480,450	269,862
Unrealized loss position for less than 12 months, unrealized loss	(593)	(420)
Unrealized loss position for more than 12 months, fair value	1,014,378	1,025,360
Unrealized loss position for more than 12 months, unrealized loss	(13,295)	(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	487,530	999,793
Unrealized loss position for less than 12 months, unrealized loss	(7,324)	(17,682)
Unrealized loss position for more than 12 months, fair value	971,658	946,166
Unrealized loss position for more than 12 months, unrealized loss	(99,490)	(125,068)
Fixed Interest Rate | US treasuries
Debt Securities, Available-for-sale [Line Items]
Unrealized loss position for less than 12 months, fair value	309,390	590,307
Unrealized loss position for less than 12 months, unrealized loss	(1,266)	(4,375)
Unrealized loss position for more than 12 months, fair value	46,048	58,523
Unrealized loss position for more than 12 months, unrealized loss	$ (154)	$ (317)