LOANS (Schedule of Loans Outstanding, by Classification) (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Total loans	$ 3,722,905	$ 3,704,440
Loans and Finance Receivables, Gross [Member] | Credit Concentration Risk [Member]
Total loans (in percent)	100.00%	100.00%
Unallocated Financing Receivables [Member]
Total loans	$ 431	$ 402
Unallocated Financing Receivables [Member] | Loans and Finance Receivables, Gross [Member] | Credit Concentration Risk [Member]
Total loans (in percent)	0.01%	0.01%
Residential Mortgage [Member] | Residential Portfolio Segment [Member]
Total loans	$ 566,463	$ 576,356
Residential Mortgage [Member] | Residential Portfolio Segment [Member] | Loans and Finance Receivables, Gross [Member] | Credit Concentration Risk [Member]
Total loans (in percent)	15.22%	15.56%
Multifamily Property [Member] | Residential Portfolio Segment [Member]
Total loans	$ 1,320,251	$ 1,388,958
Multifamily Property [Member] | Residential Portfolio Segment [Member] | Loans and Finance Receivables, Gross [Member] | Credit Concentration Risk [Member]
Total loans (in percent)	35.46%	37.49%
Commercial Mortgage [Member] | Commercial Real Estate Portfolio Segment [Member]
Total loans	$ 637,705	$ 626,656
Commercial Mortgage [Member] | Commercial Real Estate Portfolio Segment [Member] | Loans and Finance Receivables, Gross [Member] | Credit Concentration Risk [Member]
Total loans (in percent)	17.13%	16.92%
Commercial Loans [Member] | Commercial Portfolio Segment [Member]
Total loans	$ 1,066,526	$ 958,294
Commercial Loans [Member] | Commercial Portfolio Segment [Member] | Loans and Finance Receivables, Gross [Member] | Credit Concentration Risk [Member]
Total loans (in percent)	28.65%	25.87%
Home Equity Lines of Credit [Member] | Residential Portfolio Segment [Member]
Total loans	$ 55,020	$ 67,497
Home Equity Lines of Credit [Member] | Residential Portfolio Segment [Member] | Loans and Finance Receivables, Gross [Member] | Credit Concentration Risk [Member]
Total loans (in percent)	1.48%	1.82%
Consumer Loans, Including Home Equity Loans [Member] | Consumer and Other Loans [Member]
Total loans	$ 76,509	$ 86,277
Consumer Loans, Including Home Equity Loans [Member] | Consumer and Other Loans [Member] | Loans and Finance Receivables, Gross [Member] | Credit Concentration Risk [Member]
Total loans (in percent)	2.05%	2.33%