FAIR VALUE OF FINANCIAL INSTRUMENTS, Balance Sheet Groupings (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Carrying Amount [Member]
Financial Assets [Abstract]
Cash and due from banks	$ 676,723	$ 243,603
Loans, net	10,407,898	5,580,583
Accrued interest receivable	51,100	34,815
Financial Liabilities [Abstract]
Savings, money market and checking accounts	9,270,496	3,212,495
Certificates of Deposits ("CDs")	1,540,316	1,322,638
FHLBNY Advances	533,865	1,204,010
Subordinated debt, net	197,234	114,052
Other borrowings	126,763	120,000
Accrued interest payable	2,024	1,734
Fair Value [Member]
Financial Assets [Abstract]
Cash and due from banks	676,723	243,603
Loans, net	10,489,350	5,598,787
Accrued interest receivable	51,100	34,815
Financial Liabilities [Abstract]
Savings, money market and checking accounts	9,270,496	3,212,495
Certificates of Deposits ("CDs")	1,545,436	1,328,554
FHLBNY Advances	534,049	1,207,890
Subordinated debt, net	198,297	114,340
Other borrowings	126,763	120,000
Accrued interest payable	2,024	1,734
Fair Value [Member] | Level 1 Inputs [Member]
Financial Assets [Abstract]
Cash and due from banks	676,723	243,603
Accrued interest receivable		2
Financial Liabilities [Abstract]
Savings, money market and checking accounts	9,270,496	3,212,495
Other borrowings	126,763	120,000
Fair Value [Member] | Level 2 Inputs [Member]
Financial Assets [Abstract]
Accrued interest receivable	3,602	1,584
Financial Liabilities [Abstract]
Certificates of Deposits ("CDs")	1,545,436	1,328,554
FHLBNY Advances	534,049	1,207,890
Subordinated debt, net	198,297	114,340
Accrued interest payable	2,024	1,734
Fair Value [Member] | Level 3 Inputs [Member]
Financial Assets [Abstract]
Loans, net	10,489,350	5,598,787
Accrued interest receivable	$ 47,498	$ 33,229