LOANS RECEIVABLE AND CREDIT QUALITY, Troubled Debt Restructurings (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019 USD ($) Loan	Mar. 31, 2018 Loan	Dec. 31, 2018 USD ($) Loan
Troubled Debt Restructuring on Receivables [Abstract]
Number of TDRs on non-accrual status	0		0
Amount of TDRs on non-accrual status | $	$ 0		$ 0
Number of loans modified	0	0
Number of loan commitments to borrowers with outstanding TDRs	0		0
TDRs which defaulted within twelve months following the modification	0	0
Real Estate Loans [Member]
Troubled Debt Restructuring on Receivables [Abstract]
Number of loans	4		4
Balance | $	$ 4,334		$ 4,369
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 | $	$ 12		$ 14
Real Estate Loans [Member] | Multifamily Residential and Residential Mixed-Use [Member]
Troubled Debt Restructuring on Receivables [Abstract]
Number of loans	2		2
Balance | $	$ 261		$ 271
Real Estate Loans [Member] | Commercial Real Estate and Commercial Mixed-Use [Member]
Troubled Debt Restructuring on Receivables [Abstract]
Number of loans	1		1
Balance | $	$ 4,061		$ 4,084