Quarterly Financial Information (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Information (unaudited)
Revenue	$ 42,655	$ 38,587	$ 35,052	$ 28,133	$ 30,801	$ 52,488	$ 29,675	$ 9,081	$ 143,526	$ 89,571	$ 11,552
Total costs and expenses	35,806	34,277	31,976	24,703	26,072	23,321	25,919	22,503	126,762	97,815	73,939
Operating income (loss)	6,849	4,310	3,076	3,430	4,729	29,167	3,756	(13,422)
Net income (loss)	$ 6,872	$ 4,222	$ 2,005	$ 917	$ 4,354	$ 27,858	$ 3,202	$ (15,543)	$ 14,016	$ 19,871	$ (92,273)
Net income (loss) per share, basic	$ 0.14	$ 0.09	$ 0.04	$ 0.02	$ 0.10	$ 0.65	$ 0.08	$ (0.38)	$ 0.30	$ 0.47	$ (2.90)
Net income (loss) per share, diluted	$ 0.14	$ 0.08	$ 0.03	$ 0.02	$ 0.10	$ 0.39	$ 0.08	$ (0.38)	$ 0.28	$ 0.32	$ (2.90)
Revenue From Royalty Agreement						$ 30,000				$ 30,000