DERIVATIVES AND HEDGING ACTIVITIES - Narrative (Details)	3 Months Ended			9 Months Ended
	Sep. 30, 2020 USD ($)	Mar. 31, 2020	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) agreement
Derivative [Line Items]
Cumulative amount of last-of-layer fair value hedging basis adjustments	$ 10,900,000			$ 10,900,000		$ (405,000)
Carrying amount of the last-of-layer hedged assets	1,000,000,000.0			1,000,000,000.0		999,600,000
Designated as Hedging Instrument | Interest Rate Swap
Derivative [Line Items]
Closed portfolio loans used in hedging relationship	2,200,000,000			2,200,000,000		2,500,000,000
Cumulative amount of last-of-layer fair value hedging basis adjustments	10,879,000			10,879,000		$ (405,000)
Fair Value Hedging | Designated as Hedging Instrument | Interest Rate Swap
Derivative [Line Items]
Number of agreements entered into | agreement						2
Term of contract		2 years
Notional amounts	1,000,000,000			1,000,000,000		$ 1,000,000,000.0
Net effect on interest income	(3,453,000)		$ 1,406,000	(7,343,000)	$ 1,519,000
Carrying amount of the last-of-layer hedged assets	1,010,879,000			1,010,879,000		999,595,000
Cash collateral	$ 11,900,000			$ 11,900,000		$ 2,800,000