LOANS RECEIVABLE, NET - Summary of impaired loans by class of loan (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2022	Dec. 31, 2021
With no related allowance recorded:
Unpaid Principal Balance	$ 12,824	$ 14,208
Recorded Investment	12,949	14,424
Average Recorded Investment	14,050	15,630
Interest Income Recognized	172	314
Cash Basis Interest Recognized	165	298
With an allowance recorded:
Unpaid Principal Balance	1,055	1,099
Recorded Investment	1,054	1,098
Allowance for Loan Losses Allocated	28	68
Average Recorded Investment	1,057	1,284
Interest Income Recognized	12	52
Cash Basis Interest Recognized	8	48
Total
Unpaid Principal Balance	13,879	15,307
Recorded Investment	14,003	15,522
Allowance for Loan Losses Allocated	28	68
Average Recorded Investment	15,107	16,914
Interest Income Recognized	184	366
Cash Basis Interest Recognized	173	346
Residential Portfolio Segment \| Residential one-to-four family
With no related allowance recorded:
Unpaid Principal Balance	7,426	8,744
Recorded Investment	7,714	9,108
Average Recorded Investment	8,769	9,534
Interest Income Recognized	111	75
Cash Basis Interest Recognized	111	75
With an allowance recorded:
Unpaid Principal Balance	1,055	1,062
Recorded Investment	1,054	1,061
Allowance for Loan Losses Allocated	28	31
Average Recorded Investment	1,057	1,243
Interest Income Recognized	12	50
Cash Basis Interest Recognized	8	46
Total
Allowance for Loan Losses Allocated	28	31
Residential Portfolio Segment \| Multifamily
With no related allowance recorded:
Unpaid Principal Balance	672	684
Recorded Investment	671	684
Average Recorded Investment	678	1,170
Interest Income Recognized	6	26
Cash Basis Interest Recognized	4	24
With an allowance recorded:
Unpaid Principal Balance	0	0
Recorded Investment	0	0
Allowance for Loan Losses Allocated	0	0
Average Recorded Investment	0	0
Interest Income Recognized	0	0
Cash Basis Interest Recognized	0	0
Total
Allowance for Loan Losses Allocated	0	0
Nonresidential Portfolio Segment \| Non-residential
With no related allowance recorded:
Unpaid Principal Balance	4,672	4,725
Recorded Investment	4,510	4,577
Average Recorded Investment	4,548	4,869
Interest Income Recognized	54	210
Cash Basis Interest Recognized	49	196
With an allowance recorded:
Unpaid Principal Balance	0	0
Recorded Investment	0	0
Allowance for Loan Losses Allocated	0	0
Average Recorded Investment	0	0
Interest Income Recognized	0	0
Cash Basis Interest Recognized	0	0
Total
Allowance for Loan Losses Allocated	0	0
Construction and Land Portfolio Segment \| Construction
With no related allowance recorded:
Unpaid Principal Balance	0	0
Recorded Investment	0	0
Average Recorded Investment	0	0
Interest Income Recognized	0	0
Cash Basis Interest Recognized	0	0
With an allowance recorded:
Unpaid Principal Balance	0	0
Recorded Investment	0	0
Allowance for Loan Losses Allocated	0	0
Average Recorded Investment	0	0
Interest Income Recognized	0	0
Cash Basis Interest Recognized	0	0
Total
Allowance for Loan Losses Allocated	0	0
Commercial Portfolio Segment \| Commercial and industrial (including PPP)
With no related allowance recorded:
Unpaid Principal Balance	0	0
Recorded Investment	0	0
Average Recorded Investment	0	0
Interest Income Recognized	0	0
Cash Basis Interest Recognized	0	0
With an allowance recorded:
Unpaid Principal Balance	0	0
Recorded Investment	0	0
Allowance for Loan Losses Allocated	0	0
Average Recorded Investment	0	0
Interest Income Recognized	0	0
Cash Basis Interest Recognized	0	0
Total
Allowance for Loan Losses Allocated	0	0
Junior Lien Portfolio Segment \| Junior liens
With no related allowance recorded:
Unpaid Principal Balance	54	55
Recorded Investment	54	55
Average Recorded Investment	55	57
Interest Income Recognized	1	3
Cash Basis Interest Recognized	1	3
Consumer and Other Portfolio Segment \| Consumer and other
With an allowance recorded:
Unpaid Principal Balance	0	37
Recorded Investment	0	37
Allowance for Loan Losses Allocated	0	37
Average Recorded Investment	0	41
Interest Income Recognized	0	2
Cash Basis Interest Recognized	0	2
Total
Allowance for Loan Losses Allocated	$ 0	$ 37

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