SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ 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
SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED)
Revenues	$ 73,962	$ 80,092	$ 79,981	$ 76,576	$ 65,355	$ 64,968	$ 60,335	$ 61,354	$ 310,611	$ 252,012	$ 245,893
Gross profit	21,570	23,762	23,517	22,554	20,551	19,546	17,881	17,701	91,403	75,679	73,004
Net income	$ 2,636	$ 4,860	$ 4,231	$ 4,198	$ 95	$ 3,057	$ 2,227	$ 2,657	$ 15,925	$ 8,036	$ 9,078
Basic earnings per share (in dollars per share)	$ 0.28	$ 0.52	$ 0.46	$ 0.45	$ 0.01	$ 0.33	$ 0.24	$ 0.29	$ 1.72	$ 0.88	$ 1.01
Diluted earnings per share (in dollars per share)	$ 0.28	$ 0.52	$ 0.45	$ 0.45	$ 0.01	$ 0.33	$ 0.24	$ 0.29	$ 1.70	$ 0.87	$ 1.00