INVESTMENT SECURITIES - Amortized Cost and Fair Value of HTM Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Gross Unrealized Gains	$ 1,174	$ 1,296
Gross Unrealized Losses	(154,225)	(149,342)
Fair Value	1,521,621	1,549,509
Allowance for credit losses	(710)	(721)	$ (687)	$ 0
Total held-to-maturity	1,673,962	1,696,834
Traditional securities
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost	616,225	620,286
Gross Unrealized Gains	1,174	1,296
Gross Unrealized Losses	(45,400)	(46,164)
Fair Value	571,999	575,418
Allowance for credit losses	(53)	(54)
Total held-to-maturity	616,172	620,232
GSE certificates & CMOs
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost	193,070	194,329
Gross Unrealized Gains	952	1,099
Gross Unrealized Losses	(20,712)	(19,693)
Fair Value	173,310	175,735
Non-GSE certificates & CMOs
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost	78,510	79,406
Gross Unrealized Gains	0	9
Gross Unrealized Losses	(6,706)	(6,686)
Fair Value	71,804	72,729
ABS
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost	278,249	279,916
Gross Unrealized Gains	96	23
Gross Unrealized Losses	(6,519)	(8,678)
Fair Value	271,826	271,261
Municipal
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost	66,396	66,635
Gross Unrealized Gains	126	165
Gross Unrealized Losses	(11,463)	(11,107)
Fair Value	55,059	55,693
Property Assessed Clean Energy ("PACE") assessments
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost	1,058,447	1,077,269
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(108,825)	(103,178)
Fair Value	949,622	974,091
Allowance for credit losses	(657)	(667)
Total held-to-maturity	1,057,790	1,076,602
Commercial PACE assessments
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost	256,661	258,306
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(29,767)	(29,211)
Fair Value	226,894	229,095
Allowance for credit losses	(256)	(258)	(262)	0
Residential PACE assessments
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Amortized Cost	801,786	818,963
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(79,058)	(73,967)
Fair Value	722,728	744,996
Allowance for credit losses	$ (401)	$ (409)	$ (367)	$ 0