FAIR VALUE OF FINANCIAL INSTRUMENTS - Balance Sheet Groupings (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Carrying Amount
Financial Assets [Abstract]
Cash and due from banks	$ 1,184,183	$ 243,603
Loans, net	9,453,871	5,580,583
Accrued interest receivable	47,209	34,815
Financial Liabilities [Abstract]
Savings, money market and checking accounts	9,765,228	3,212,495
Certificates of Deposits ("CDs")	1,300,965	1,322,638
FHLBNY Advances	25,000	1,204,010
Subordinated debt, net	197,188	114,052
Other borrowings	1,841	120,000
Accrued interest payable	1,068	1,734
Fair Value
Financial Assets [Abstract]
Cash and due from banks	1,184,183	243,603
Loans, net	9,523,466	5,598,787
Accrued interest receivable	47,209	34,815
Financial Liabilities [Abstract]
Savings, money market and checking accounts	9,765,228	3,212,495
Certificates of Deposits ("CDs")	1,307,876	1,328,554
FHLBNY Advances	25,013	1,207,890
Subordinated debt, net	203,201	114,340
Other borrowings	1,841	120,000
Accrued interest payable	1,068	1,734
Fair Value | Level 1 Inputs [Member]
Financial Assets [Abstract]
Cash and due from banks	1,184,183	243,603
Accrued interest receivable		2
Financial Liabilities [Abstract]
Savings, money market and checking accounts	9,765,228	3,212,495
Other borrowings	1,841	120,000
Fair Value | Level 2 Inputs [Member]
Financial Assets [Abstract]
Accrued interest receivable	3,415	1,584
Financial Liabilities [Abstract]
Certificates of Deposits ("CDs")	1,307,876	1,328,554
FHLBNY Advances	25,013	1,207,890
Subordinated debt, net	203,201	114,340
Accrued interest payable	1,068	1,734
Fair Value | Level 3 Inputs [Member]
Financial Assets [Abstract]
Loans, net	9,523,466	5,598,787
Accrued interest receivable	$ 43,794	$ 33,229