COMMITMENTS AND CONTINGENCIES AND OTHER MATTERS - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Commitments and Contingencies [Line Items]
Rental expenses under leases	$ 6,900	$ 7,300	$ 6,800
Federal funds purchased		$ 50,000
BNB Bank (Bank)
Commitments and Contingencies [Line Items]
Required cash balance with Federal Reserve Bank of New York	12,700
Average balance maintained	50,900
Lines of credit with unaffiliated correspondent banks to provide short-term credit	373,000
Amount available for transactions under Master Repurchase Agreement	1,400,000
BNB Bank (Bank) | Federal Home Loan Bank Advances
Commitments and Contingencies [Line Items]
Lines of credit available on an unsecured basis	353,000
Federal funds purchased	$ 0