UNAUDITED SELECTED QUARTERLY FINANCIAL DATA: (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 244,781	$ 234,871	$ 225,240	$ 212,514	$ 224,867	$ 223,312	$ 217,267	$ 214,801	$ 917,406	$ 880,247	$ 850,088
Gross profit	123,297	118,951	110,168	98,554	106,573	106,844	97,162	91,982	450,970	402,561	361,706
Loss from operations	4,795	11,058	453	(5,707)	(8,709)	9,115	7,120	8,162	10,599	15,689	(13,063)
Net earnings (loss)	$ 5,175	$ 22,941	$ (3,336)	$ (1,300)	$ (8,081)	$ 1,073	$ 7,140	$ 3,976	$ 23,480	$ 4,108	$ 6,703
Basic earnings (loss) per share:
Net basic earnings (loss) (in dollars per share)	$ 0.07	$ 0.29	$ (0.04)	$ (0.02)	$ (0.10)	$ 0.01	$ 0.09	$ 0.05	$ 0.30	$ 0.05	$ 0.09
Diluted earnings (loss) per share:
Net diluted earnings (loss) per share (in dollars per share)	$ 0.06	$ 0.28	$ (0.04)	$ (0.02)	$ (0.10)	$ 0.01	$ 0.09	$ 0.05	$ 0.29	$ 0.05	$ 0.09