LOANS (Schedule of Loans Outstanding, by Classification) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Total loans	$ 3,667,197	$ 3,312,144
Construction Loans [Member]
Total loans		1,405
Residential Portfolio Segment [Member] | Residential Mortgage [Member]
Total loans	602,775	527,370
Residential Portfolio Segment [Member] | Multifamily Property [Member]
Total loans	1,441,852	1,459,594
Residential Portfolio Segment [Member] | Home Equity Lines of Credit [Member]
Total loans	68,787	65,682
Commercial Real Estate Portfolio Segment [Member] | Commercial Mortgage [Member]
Total loans	625,466	551,233
Commercial Portfolio Segment [Member] | Commercial Loans [Member]
Total loans	845,831	636,714
Consumer and Other [Member] | Consumer Loans, Including Home Equity Loans [Member]
Total loans	81,671	69,654
Unallocated Financing Receivables [Member]
Total loans	$ 815	$ 492
Loans and Finance Receivables [Member]
Total loans (in percent)	100.00%	100.00%
Loans and Finance Receivables [Member] | Construction Loans [Member]
Total loans (in percent)		0.04%
Loans and Finance Receivables [Member] | Residential Portfolio Segment [Member] | Residential Mortgage [Member]
Total loans (in percent)	16.44%	15.92%
Loans and Finance Receivables [Member] | Residential Portfolio Segment [Member] | Multifamily Property [Member]
Total loans (in percent)	39.32%	44.07%
Loans and Finance Receivables [Member] | Residential Portfolio Segment [Member] | Home Equity Lines of Credit [Member]
Total loans (in percent)	1.88%	1.98%
Loans and Finance Receivables [Member] | Commercial Real Estate Portfolio Segment [Member] | Commercial Mortgage [Member]
Total loans (in percent)	17.05%	16.65%
Loans and Finance Receivables [Member] | Commercial Portfolio Segment [Member] | Commercial Loans [Member]
Total loans (in percent)	23.06%	19.23%
Loans and Finance Receivables [Member] | Consumer and Other [Member] | Consumer Loans, Including Home Equity Loans [Member]
Total loans (in percent)	2.23%	2.10%
Loans and Finance Receivables [Member] | Unallocated Financing Receivables [Member]
Total loans (in percent)	0.02%	0.01%