FAIR VALUE OF FINANCIAL INSTRUMENTS, Balance Sheet Groupings (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Carrying Amount [Member]
Financial Assets [Abstract]
Cash and due from banks	$ 143,473	$ 147,256
Loans, net	5,484,495	5,372,036
Accrued interest receivable	18,868	17,875
Financial Liabilities [Abstract]
Savings, money market and checking accounts	2,826,844	2,946,717
Certificates of Deposits ("CDs")	1,580,778	1,410,037
Escrow and other deposits	137,116	85,234
FHLBNY Advances	1,087,325	1,125,350
Subordinated debt, net	113,796	113,759
Other borrowings	45,000
Accrued interest payable	4,352	2,710
Fair Value [Member]
Financial Assets [Abstract]
Cash and due from banks	143,473	147,256
Loans, net	5,410,989	5,301,281
Accrued interest receivable	18,868	17,875
Financial Liabilities [Abstract]
Savings, money market and checking accounts	2,826,844	2,946,717
Certificates of Deposits ("CDs")	1,577,338	1,407,747
Escrow and other deposits	137,116	85,234
FHLBNY Advances	1,085,118	1,119,548
Subordinated debt, net	112,089	110,346
Other borrowings	45,000
Accrued interest payable	4,352	2,710
Fair Value [Member] | Level 1 Inputs [Member]
Financial Assets [Abstract]
Cash and due from banks	143,473	147,256
Loans, net	0	0
Accrued interest receivable	27	0
Financial Liabilities [Abstract]
Savings, money market and checking accounts	2,826,844	2,946,717
Certificates of Deposits ("CDs")	0	0
Escrow and other deposits	137,116	85,234
FHLBNY Advances	0	0
Subordinated debt, net	0	0
Other borrowings	45,000
Accrued interest payable	10	0
Fair Value [Member] | Level 2 Inputs [Member]
Financial Assets [Abstract]
Cash and due from banks	0	0
Loans, net	0	0
Accrued interest receivable	1,664	1,296
Financial Liabilities [Abstract]
Savings, money market and checking accounts	0	0
Certificates of Deposits ("CDs")	1,577,338	1,407,747
Escrow and other deposits	0	0
FHLBNY Advances	1,085,118	1,119,548
Subordinated debt, net	112,089	110,346
Other borrowings	0
Accrued interest payable	4,342	2,710
Fair Value [Member] | Level 3 Inputs [Member]
Financial Assets [Abstract]
Cash and due from banks	0	0
Loans, net	5,410,989	5,301,281
Accrued interest receivable	17,177	16,579
Financial Liabilities [Abstract]
Savings, money market and checking accounts	0	0
Certificates of Deposits ("CDs")	0	0
Escrow and other deposits	0	0
FHLBNY Advances	0	0
Subordinated debt, net	0	0
Other borrowings	0
Accrued interest payable	$ 0	$ 0