LOANS AND LEASES (Schedule of Loans Outstanding, by Type of Loan) (Details) - USD ($) $ in Thousands		3 Months Ended	12 Months Ended
		Mar. 31, 2021	Dec. 31, 2020
Total loans		$ 4,377,931	$ 4,372,437
Loans and Finance Receivables, Gross [Member] | Credit Concentration Risk [Member]
Total loans (in percent)		100.00%	100.00%
Unallocated Financing Receivables [Member]
Total loans		$ 200	$ 226
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		$ 489,665	$ 502,829
Residential Mortgage [Member] | Residential Portfolio Segment [Member] | Loans and Finance Receivables, Gross [Member] | Credit Concentration Risk [Member]
Total loans (in percent)		11.18%	11.50%
Multifamily Property [Member] | Residential Portfolio Segment [Member]
Total loans		$ 1,178,940	$ 1,126,946
Multifamily Property [Member] | Residential Portfolio Segment [Member] | Loans and Finance Receivables, Gross [Member] | Credit Concentration Risk [Member]
Total loans (in percent)		26.93%	25.77%
Commercial Mortgage [Member] | Commercial Real Estate Portfolio Segment [Member]
Total loans		$ 697,599	$ 691,294
Commercial Mortgage [Member] | Commercial Real Estate Portfolio Segment [Member] | Loans and Finance Receivables, Gross [Member] | Credit Concentration Risk [Member]
Total loans (in percent)		15.94%	15.81%
Commercial Loans Including Equipment Financing [Member] | Commercial Real Estate Portfolio Segment [Member]
Total loans	[1]	$ 1,911,520	$ 1,950,981
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]	43.66%	44.62%
Construction [Member] | Commercial Portfolio Segment [Member]
Total loans		$ 17,865	$ 12,600
Construction [Member] | Commercial Portfolio Segment [Member] | Loans and Finance Receivables, Gross [Member] | Credit Concentration Risk [Member]
Total loans (in percent)		0.41%	0.29%
Home Equity Lines of Credit [Member] | Residential Portfolio Segment [Member]
Total loans		$ 45,623	$ 50,545
Home Equity Lines of Credit [Member] | Residential Portfolio Segment [Member] | Loans and Finance Receivables, Gross [Member] | Credit Concentration Risk [Member]
Total loans (in percent)		1.04%	1.15%
Consumer Loans, Including Home Equity Loans [Member] | Consumer and Other Loans [Member]
Total loans		$ 36,519	$ 37,016
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)		0.83%	0.85%

[1] Includes PPP loans of $187 million at March 31, 2021 and $196 million at December 31, 2020.