EQUITY AWARDS - Schedule of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Number of Shares
Outstanding at beginning of year (in shares)	506,200	508,000	508,000
Effect of 10% stock dividend (in shares)	50,770
Granted (in shares)	45,500	39,000
Exercised (in shares)	(48,630)	(3,000)
Forfeited (in shares)	(19,020)	(37,600)
Balance (in shares)	534,820	506,400	506,200	508,000
Exercisable
Outstanding (in shares)	307,786	302,220
Weighted-average exercise price (in USD per share)	$ 23.78	$ 25.55
Weighted-average remaining contractual life in years	4 years 3 months 29 days	4 years 9 months 7 days
Aggregate intrinsic value	$ 3,715	$ 244
Weighted-Average Exercise Price
Outstanding at beginning of year (in USD per share)	$ 26.81	$ 26.68	$ 26.68
Granted (in USD per share)	33.49	27.43
Exercised (in USD per share)	22.89	24.00
Forfeited (in USD per share)	26.01	29.68
Balance (in USD per share)	$ 25.22	$ 26.53	$ 26.81	$ 26.68
Weighted-Average Remaining Contractual Life in Years
Outstanding	5 years 6 months 10 days	5 years 7 months 13 days	5 years 9 months 25 days	6 years 2 months 26 days
Granted	9 years 7 months 2 days	9 years 6 months 3 days
Exercised	3 years 9 months 25 days	2 years 14 days
Forfeited	6 years 10 months 2 days	8 years 1 month 13 days
Aggregate Intrinsic Value
Outstanding	$ 1,805	$ 3,159	$ 3,159
Granted	107	24
Exercised	630	3
Forfeited	187	24
Outstanding	$ 5,684	$ 304	$ 1,805	$ 3,159