LOANS RECEIVABLE - Summary of loans receivable (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022	Dec. 31, 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans		$ 1,542,380
Deferred fees, costs and premiums and discounts, net		2,747
Total loans	$ 1,586,060	1,545,127
Allowance for loan losses	(14,153)	(13,400)	$ (13,465)	$ (14,425)
Loans receivable, net	1,571,907	1,531,727
Residential one-to-four family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		597,254
Multifamily
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		690,690
Non-residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		216,061
Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		17,799
Junior liens
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		18,631
Commercial and industrial (including PPP)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		4,653
Consumer and other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans		39
Residential Portfolio Segment | Residential one-to-four family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans		594,521
Total loans	592,809	597,254
Allowance for loan losses	(2,056)	(2,264)	(2,610)	(2,822)
Residential Portfolio Segment | Multifamily
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans		690,278
Total loans	695,207	690,690
Allowance for loan losses	(7,191)	(5,491)	(4,776)	(5,263)
Nonresidential Portfolio Segment | Non-residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans		216,394
Total loans	239,844	216,061
Allowance for loan losses	(3,570)	(3,357)	(3,465)	(2,846)
Construction and Land Portfolio Segment | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans		17,990
Total loans	28,141	17,799
Junior Lien Portfolio Segment | Junior liens
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans		18,477
Total loans	19,644	18,631
Allowance for loan losses	(46)	(451)	(549)	(636)
Commercial Portfolio Segment | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses	(1,190)	(1,697)	$ (1,905)	$ (2,678)
Commercial Portfolio Segment | Commercial and industrial (including PPP)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans		4,682
Total loans	10,357	4,653
Commercial Portfolio Segment | PPP Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans		477
Total loans	395
Consumer and Other Portfolio Segment | Consumer and other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans		38
Total loans	$ 58	$ 39