SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Earnings Per Share (Details) - $ / shares shares in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Shares
Basic (in shares)									17,846	17,585	17,305
Effect of dilutive stock options (in shares)									728	782	359
Diluted (in shares)									18,574	18,367	17,664
Per Share Amount
Basic (in dollars per share)	$ 0.40	$ 0.61	$ 0.52	$ 0.38	$ 0.25	$ 0.51	$ 0.41	$ 0.28	$ 1.91	$ 1.45	$ 1.42
Effect of dilutive stock options (in dollars per share)									(0.08)	(0.06)	(0.03)
Diluted (in dollars per share)	$ 0.39	$ 0.58	$ 0.50	$ 0.36	$ 0.23	$ 0.49	$ 0.40	$ 0.27	$ 1.83	$ 1.39	$ 1.39