CONDENSED FINANCIAL STATEMENTS OF PARENT COMPANY - Condensed Statements of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2021	Dec. 31, 2020
Condensed Cash Flow Statements, Captions [Line Items]
Net loss	$ (36,342)	$ (36,342)	$ (31,506)
Adjustments to reconcile net income to net cash provided by operating activities:
Issuance of common shares donated to Blue Foundry Charitable Foundation		7,500	0
Goodwill impairment		0	15,460
ESOP expense		1,274	0
Increase in other assets		2,134	(997)
Increase in other liabilities		4,325	707
Net cash used by operating activities		(14,142)	(1,252)
Cash flows from investing activities
Net cash used in investing activities		(105,334)	101,393
Cash flows from financing activities
Proceeds from issuance of common shares		250,780	0
Net Cash Provided by (Used in) Financing Activities		(3,523)	92,270
Net increase (decrease) in cash and cash equivalents		(122,999)	192,411
Cash and cash equivalents at beginning of period		316,445	124,034
Cash and cash equivalents at end of period	193,446	193,446	316,445
Parent Company
Condensed Cash Flow Statements, Captions [Line Items]
Net loss		(36,342)	(31,506)
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed earnings of subsidiary		27,048	18,258
Issuance of common shares donated to Blue Foundry Charitable Foundation		7,500	0
Goodwill impairment		0	13,100
ESOP expense		361	0
Increase in other assets		(82)	(5)
Increase in other liabilities		237	55
Net cash used by operating activities		(1,278)	(98)
Cash flows from investing activities
Capital contribution to banking subsidiary		(136,481)	0
Loan to ESOP		(22,818)	0
Repayment of ESOP loan		981	0
Net cash used in investing activities		(158,318)	0
Cash flows from financing activities
Proceeds from issuance of common shares		273,598	0
Net Cash Provided by (Used in) Financing Activities		273,598	0
Net increase (decrease) in cash and cash equivalents		114,002	(98)
Cash and cash equivalents at beginning of period		329	427
Cash and cash equivalents at end of period	$ 114,331	$ 114,331	$ 329