Collaboration Agreements (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Collaboration agreement
Revenue	$ 34,266	$ 27,609	$ 62,363	$ 36,604
Payables	4,518		4,518		$ 1,863
United Therapeutics
Collaboration agreement
Commercial milestone payments received	3,500		3,500
Revenue From Royalty Agreement					30,000
Revenue	0	$ 2,000	0	2,000
Receivables	0		0		0
Payables	0		0		0
Stendhal License
Collaboration agreement
Amount received to be recognized as revenue on a straight-line basis	1,500		1,500
Future milestone payment to be received, based on certain milestones defined in the license agreement	1,500		1,500
Collaborative Arrangement | Stendhal License
Collaboration agreement
Revenue			800	$ 100
Amount received to be recognized as revenue on a straight-line basis	1,800		$ 1,800
Collaboration agreement substantive obligation period			12 years
Deferred revenue	1,300		$ 1,300		$ 1,400
Deferred revenue current	100		100
Deferred revenue Non-current	1,200		1,200
Future milestone payment to be received, based on certain milestones defined in the license agreement	1,800		1,800
Combined amount of milestone and product receivables	$ 800		$ 800