SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED)
Revenues	$ 87,925	$ 96,633	$ 92,630	$ 93,896	$ 73,962	$ 80,092	$ 79,981	$ 76,576	$ 371,084	$ 310,611	$ 252,012
Gross profit	26,470	30,030	28,422	27,662	21,570	23,762	23,517	22,554	112,584	91,403	75,679
Net income	$ 3,489	$ 4,618	$ 4,445	$ 4,470	$ 2,636	$ 4,860	$ 4,231	$ 4,198	$ 17,022	$ 15,925	$ 8,036
Basic earnings per share (in dollars per share)	$ 0.37	$ 0.49	$ 0.47	$ 0.48	$ 0.28	$ 0.52	$ 0.46	$ 0.45	$ 1.81	$ 1.72	$ 0.88
Diluted earnings per share (in dollars per share)	$ 0.37	$ 0.49	$ 0.47	$ 0.48	$ 0.28	$ 0.52	$ 0.45	$ 0.45	$ 1.80	$ 1.70	$ 0.87