LOANS, ALLOWANCE FOR LOAN LOSSES AND IMPAIRED LOANS - Non-Accretable Yield (Details) - Acquired Loans - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Non-Accretable Yield Movement Schedule [Roll Forward]
Balance at beginning of period	$ 1,087	$ 6,290
Additions to non-accretable difference for acquired purchased credit impaired loans	0	0
Non-accretable difference realized as interest from payoffs of purchased credit impaired loans	(103)	(1,693)
Transfers from non-accretable difference to accretable discount	(298)	(2,754)
Non-accretable difference used to reduce loan principal balance	0	(505)
Non-accretable difference transferred to OREO due to loan foreclosure	0	(251)
Balance at end of period	$ 686	$ 1,087