LOANS AND LEASES (Schedule of Loans Outstanding, by Type of Loan) (Details) - USD ($) $ in Thousands		9 Months Ended	12 Months Ended
		Sep. 30, 2020	Dec. 31, 2019
Total loans		$ 4,430,651	$ 4,394,137
Loans and Finance Receivables, Gross [Member] | Credit Concentration Risk [Member]
Total loans (in percent)		100.00%	100.00%
Unallocated Financing Receivables [Member]
Total loans		$ 260	$ 349
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		$ 518,335	$ 549,138
Residential Mortgage [Member] | Residential Portfolio Segment [Member] | Loans and Finance Receivables, Gross [Member] | Credit Concentration Risk [Member]
Total loans (in percent)		11.70%	12.50%
Multifamily Property [Member] | Residential Portfolio Segment [Member]
Total loans		$ 1,168,796	$ 1,210,003
Multifamily Property [Member] | Residential Portfolio Segment [Member] | Loans and Finance Receivables, Gross [Member] | Credit Concentration Risk [Member]
Total loans (in percent)		26.38%	27.54%
Commercial Mortgage [Member] | Commercial Real Estate Portfolio Segment [Member]
Total loans		$ 722,678	$ 761,244
Commercial Mortgage [Member] | Commercial Real Estate Portfolio Segment [Member] | Loans and Finance Receivables, Gross [Member] | Credit Concentration Risk [Member]
Total loans (in percent)		16.31%	17.32%
Commercial Loans Including Equipment Financing [Member] | Commercial Real Estate Portfolio Segment [Member]
Total loans	[1]	$ 1,909,724	$ 1,756,477
Commercial Loans Including Equipment Financing [Member] | Commercial Real Estate Portfolio Segment [Member] | Loans and Finance Receivables, Gross [Member] | Credit Concentration Risk [Member]
Total loans (in percent)	[1]	43.10%	39.97%
Construction [Member] | Commercial Portfolio Segment [Member]
Total loans		$ 6,805	$ 5,306
Construction [Member] | Commercial Portfolio Segment [Member] | Loans and Finance Receivables, Gross [Member] | Credit Concentration Risk [Member]
Total loans (in percent)		0.15%	0.12%
Home Equity Lines of Credit [Member] | Residential Portfolio Segment [Member]
Total loans		$ 52,194	$ 57,248
Home Equity Lines of Credit [Member] | Residential Portfolio Segment [Member] | Loans and Finance Receivables, Gross [Member] | Credit Concentration Risk [Member]
Total loans (in percent)		1.18%	1.30%
Consumer Loans, Including Home Equity Loans [Member] | Consumer and Other Loans [Member]
Total loans		$ 51,859	$ 54,372
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)		1.17%	1.24%

[1] The September 30, 2020 balance includes PPP loans of $202.0 million