SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Earnings Per Share (Details) - $ / shares shares in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Shares
Basic (in shares)									17,585	17,305	16,948
Effect of dilutive stock options (in shares)									782	359	387
Diluted (in shares)									18,367	17,664	17,335
Per Share Amount
Basic (in dollars per share)	$ 0.25	$ 0.51	$ 0.41	$ 0.28	$ 0.37	$ 0.45	$ 0.33	$ 0.27	$ 1.45	$ 1.42	$ 1.22
Effect of dilutive stock options (in dollars per share)									(0.06)	(0.03)	(0.03)
Diluted (in dollars per share)	$ 0.23	$ 0.49	$ 0.40	$ 0.27	$ 0.36	$ 0.45	$ 0.32	$ 0.26	$ 1.39	$ 1.39	$ 1.19