LOANS RECEIVABLE AND CREDIT QUALITY, Troubled Debt Restructurings (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) Loan	Dec. 31, 2017 USD ($) Loan	Dec. 31, 2016 USD ($) Loan
Troubled Debt Restructuring on Receivables [Abstract]
Number of TDRs on non-accrual status	0	0
Number of loans modified	0	0
Allocated allowance on TDRs | $	$ 0	$ 0
Number of loan commitments to borrowers with outstanding TDRs	0	0
TDRs which defaulted within twelve months following the modification	0	0	0
Minimum [Member]
Troubled Debt Restructuring on Receivables [Abstract]
Short term extensions grant period	6 months
Maximum [Member]
Troubled Debt Restructuring on Receivables [Abstract]
Short term extensions grant period	12 months
Real Estate Loans [Member]
Troubled Debt Restructuring on Receivables [Abstract]
Number of loans	4	6
Balance | $	$ 4,369	$ 8,111
Real Estate Loans [Member] | One- to Four-Family Residential, Including Condominium and Cooperative Apartment [Member]
Troubled Debt Restructuring on Receivables [Abstract]
Number of loans	1	1
Balance | $	$ 14	$ 22
Number of loans modified			1
Pre-modification outstanding recorded investment | $			$ 33
Post-modification outstanding recorded investment | $			$ 33
Real Estate Loans [Member] | Multifamily Residential and Residential Mixed-Use [Member]
Troubled Debt Restructuring on Receivables [Abstract]
Number of loans	2	3
Balance | $	$ 271	$ 619
Real Estate Loans [Member] | Commercial Real Estate and Commercial Mixed-Use [Member]
Troubled Debt Restructuring on Receivables [Abstract]
Number of loans	1	2
Balance | $	$ 4,084	$ 7,470