LEASES - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jan. 28, 2021	Nov. 30, 2020
Lessee, Lease, Description [Line Items]
Operating lease, weighted average remaining lease term (years)	10 years 3 months 18 days
Operating lease, weighted average discount rate	3.39%
Rent expense	$ 1,000,000.0	$ 1,000,000.0
Rent expense			$ 1,100,000
Operating lease, liability, termination					$ 200,000
Operating lease not yet commenced	0
Operating lease right-of-use assets	7,145,000	8,001,000
Operating lease liabilities	$ 7,264,000	$ 8,084,000
Finance lease, weighted average remaining lease term (years)	12 years 1 month 6 days
Finance lease, weighted average discount rate	3.36%
Finance lease not yet commenced	$ 0
Branch Location, Western New York Location | Subsequent Event
Lessee, Lease, Description [Line Items]
Operating lease, term (in years)				3 years
Operating lease right-of-use assets				$ 100,000
Operating lease liabilities				$ 100,000