FAIR VALUE - Summary of assets measured at level 3 fair value on recurring basis (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Summary of assets measured on a recurring and nonrecurring basis
Other real estate owned valuation allowance		$ 1,900
Impaired Financing Receivable, with Related Allowance, Recorded Investment	$ 2,262	3,421
Loans and Leases Receivable, Allowance	12,964	12,539
Other real estate owned, gross		2,100
Other real estate owned		194
Net recorded investment	488	1,958
Level 3
Summary of assets measured on a recurring and nonrecurring basis
Impaired Financing Receivable, with Related Allowance, Recorded Investment	2,300	3,400
Loans and Leases Receivable, Allowance	1,800	1,600
Provision for loan losses	1,800	1,600
Commercial properties | Nonrecurring
Summary of assets measured on a recurring and nonrecurring basis
Other real estate owned		194
Commercial properties | Level 3 | Nonrecurring
Summary of assets measured on a recurring and nonrecurring basis
Other real estate owned		194
Commercial and Industrial | Nonrecurring
Summary of assets measured on a recurring and nonrecurring basis
Net recorded investment	479	1,800
Commercial and Industrial | Level 3 | Nonrecurring
Summary of assets measured on a recurring and nonrecurring basis
Net recorded investment	$ 479	$ 1,800