CHANGE IN ACCUMULATED OTHER COMPREHENSIVE LOSS - Components of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			$ 2,205,113
Other comprehensive loss (income)	$ (41,950)	$ (205,059)	11,401	$ (480,919)
Less: Amounts reclassified from accumulated other comprehensive loss	4,306	(39)	8,384	(191)
Net current-period other comprehensive (loss) income	(37,644)	(205,098)	19,785	(481,110)
Ending balance	2,314,659		2,314,659
Amortization of unrealized losses on securities reclassified to held-to-maturity, tax expense	(1,386)	37,830	(2,702)	37,839
Fannie Mae (FNMA) mortgage-backed securities (MBS)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amortization of unrealized losses on securities reclassified to held-to-maturity, tax expense		119,800		119,800
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(618,415)	(313,780)	(675,844)	(37,768)
Ending balance	(656,059)	(518,878)	(656,059)	(518,878)
Net change in investment securities available-for-sale
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(510,523)	(309,791)	(563,533)	(33,873)
Other comprehensive loss (income)	(40,367)	(85,422)	12,643	(361,340)
Less: Amounts reclassified from accumulated other comprehensive loss	0	0	0	0
Net current-period other comprehensive (loss) income	(40,367)	(85,422)	12,643	(361,340)
Ending balance	(550,890)	(395,213)	(550,890)	(395,213)
Net change in investment securities held-to-maturity
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(104,338)	147	(108,503)	175
Other comprehensive loss (income)	0	(119,824)	0	(119,768)
Less: Amounts reclassified from accumulated other comprehensive loss	4,393	28	8,558	(56)
Net current-period other comprehensive (loss) income	4,393	(119,796)	8,558	(119,824)
Ending balance	(99,945)	(119,649)	(99,945)	(119,649)
Net change in defined benefit plan
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(4,517)	(4,718)	(4,482)	(4,691)
Other comprehensive loss (income)	(7)	(1)	5	0
Less: Amounts reclassified from accumulated other comprehensive loss	(47)	(27)	(94)	(55)
Net current-period other comprehensive (loss) income	(54)	(28)	(89)	(55)
Ending balance	(4,571)	(4,746)	(4,571)	(4,746)
Net change in fair value of derivatives used for cash flow hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	400	229	108	268
Other comprehensive loss (income)	(1,475)	0	(1,143)	1
Less: Amounts reclassified from accumulated other comprehensive loss	(40)	(40)	(80)	(80)
Net current-period other comprehensive (loss) income	(1,515)	(40)	(1,223)	(79)
Ending balance	(1,115)	189	(1,115)	189
Net change in equity method investments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	563	353	566	353
Other comprehensive loss (income)	(101)	188	(104)	188
Less: Amounts reclassified from accumulated other comprehensive loss	0	0	0	0
Net current-period other comprehensive (loss) income	(101)	188	(104)	188
Ending balance	$ 462	$ 541	$ 462	$ 541