Quarterly Results of Operations (unaudited) - Schedule of Quarterly Results of Operations (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 Results of Operations (unaudited)
Total Revenue	$ 54,506	$ 51,126	$ 45,694	$ 41,965	$ 47,597	$ 43,648	$ 54,293	$ 46,767	$ 193,291	$ 192,304	$ 241,443
Gross profit	35,908	36,646	32,048	29,912	31,954	30,050	36,551	32,104	134,514	130,657	143,540
Operating costs	34,730	31,534	32,448	29,610	29,765	29,138	33,165	28,990	128,322	121,058	93,087
Operating income (loss)	1,178	5,112	(400)	302	2,186	912	3,386	3,115	6,192	9,599	50,453
Net income (loss)	$ (25,837)	$ 2,755	$ 110	$ 573	$ 5,012	$ 478	$ 2,825	$ 2,199	$ (22,399)	$ 10,514	$ 42,151
Net income/(loss) per share:
Basic (in dollars per share)	$ (0.65)	$ 0.07	$ 0.00	$ 0.01	$ 0.13	$ 0.01	$ 0.07	$ 0.06	$ (0.56)	$ 0.27	$ 1.07
Diluted (in dollars per share)	$ (0.65)	$ 0.07	$ 0.00	$ 0.01	$ 0.13	$ 0.01	$ 0.07	$ 0.06	$ (0.56)	$ 0.27	$ 1.06