DERIVATIVES - Narrative (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) contract	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) contract	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Derivative [Line Items]
Notional amounts	$ 1,100,000		$ 1,100,000		$ 823,900
Derivative liability position net	0		0
Derivative asset position net	68,000		68,000
Collateral received against obligations in net asset position	69,100		69,100
Collateral posted in net liability position	0		0
Derivative designated as a cash flow hedge | Reclassifications out of accumulated other comprehensive (loss) income
Derivative [Line Items]
Accelerated reclassification, loss from other comprehensive income to earnings as a result of the hedged forecasted transactions becoming probable not to occur	3,300
Interest rate swaps | Derivative designated as a cash flow hedge
Derivative [Line Items]
Notional amounts	280,000		280,000		$ 290,000
Notional amount terminated	$ 125,000		$ 125,000
Derivative, number of terminations | contract	4		4
Loss on termination of swaps, reported in non-interest income	$ 3,400		$ 3,400
Interest income (expense) on derivative	(4,300)	$ 331	(4,400)	$ 1,400
Interest income (expenses) recorded on swap transactions	$ (4,325)	$ 331	(4,414)	$ 1,353
Interest rate swaps | Derivative designated as a cash flow hedge | Federal Home Loan Bank of New York
Derivative [Line Items]
Reclassified as an increase to interest expense during the next twelve months			2,200
Interest rate swaps | Derivative designated as a cash flow hedge | Federal Home Loan Bank of New York | Reclassifications out of accumulated other comprehensive (loss) income
Derivative [Line Items]
Increase to interest expense			$ 4,400