DERIVATIVES AND HEDGING ACTIVITIES - Narrative (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Derivative [Line Items]
Liability for cash collateral received from counterparties	$ 6,900	$ 15,200
Receivable for cash collateral paid to counterparties	16,700	2,900
Notional amount of open interest rate swap agreements	2,562,963	3,696,733
Interest rate swaps, back-to-back [Member]
Derivative [Line Items]
Notional amount of open interest rate swap agreements	$ 217,000	$ 144,000