DERIVATIVE FINANCIAL INSTRUMENTS AND HEDGING ACTIVITIES - Additional information (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($) item	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) item	Sep. 30, 2020 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Apr. 30, 2020 USD ($)	Dec. 31, 2019 USD ($) item	Nov. 30, 2019 USD ($)
Derivative [Line Items]
Acquisition, conversion and other expenses	$ 318	$ 691	$ 1,759	$ 952
Notional amount of interest rate swap	$ 929,882		$ 929,882			$ 876,603
Interest rate swap on variable rate loans
Derivative [Line Items]
Variable rate loan assets					$ 50,000
Interest rate swap on variable rate loans | LIBOR less two days
Derivative [Line Items]
Variable interest rate					0.806%
Interest rate swap on deposits
Derivative [Line Items]
Derivative, Number of Instruments Held | item	2		2
Term of interest rate swap			5 years
Fixed rate of interest rate swap							0.59%		1.53%
Notional amount of interest rate swap							$ 25,000		$ 50,000
Designated as hedging instrument | Cash flow hedges
Derivative [Line Items]
Notional amount of interest rate swap	$ 125,000		$ 125,000			75,000
Designated as hedging instrument | Cash flow hedges | Interest rate cap agreements
Derivative [Line Items]
Notional amount of interest rate swap	75,000		75,000			75,000
Designated as hedging instrument | Cash flow hedges | Interest rate swap on variable rate loans
Derivative [Line Items]
Notional amount of interest rate swap	50,000		50,000
Designated as hedging instrument | Fair value hedges
Derivative [Line Items]
Notional amount of interest rate swap	37,190		37,190			37,190
Designated as hedging instrument | Fair value hedges | Interest rate swap on deposits
Derivative [Line Items]
Derivative, Number of Instruments Held | item								8
Notional amount of interest rate swap	$ 37,190		$ 37,190			$ 37,190		$ 37,200
Fixed interest rate, weighted average								1.696%