SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Earnings Per Share (Details) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Shares
Basic (in shares)	18,218	18,025	17,846
Effect of dilutive stock options (in shares)	659	659	728
Diluted (in shares)	18,877	18,684	18,574
Per Share Amount
Basic (in dollars per share)	$ 1.30	$ 1.77	$ 1.91
Effect of dilutive stock options (in dollars per share)	(0.05)	(0.07)	(0.08)
Diluted (in dollars per share)	$ 1.25	$ 1.70	$ 1.83