QUARTERLY CONSOLIDATED FINANCIAL DATA (UNAUDITED) (Schedule of Quarterly Financial Information) (Details) - USD ($) $ / shares in Units, $ 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
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 131,237	$ 158,149	$ 194,894	$ 212,677	$ 108,947	$ 124,571	$ 149,823	$ 162,110	$ 696,957	$ 545,451	$ 462,609
Gross margin	69,711	85,792	105,797	114,447	57,347	66,877	80,681	83,552	375,747	288,457
Net income	$ 10,926	$ 15,027	$ 24,435	$ 7,484	$ 8,850	$ 7,949	$ 16,118	$ 2,552	$ 57,872	$ 35,469	$ 26,143
Basic income per common share	$ 0.36	$ 0.50	$ 0.82	$ 0.25	$ 0.30	$ 0.27	$ 0.55	$ 0.09	$ 1.93	$ 1.20	$ 0.90
Diluted income per common share	$ 0.36	$ 0.49	$ 0.80	$ 0.25	$ 0.29	$ 0.27	$ 0.54	$ 0.09	$ 1.90	$ 1.19	$ 0.89