Liability Related to Sale of Future Royalties, net - Activity within Liability Account (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Liability For Sale Of Future Royalties [Roll Forward]
Non-cash interest expense on liability related to sale of future royalties	$ 11,570	$ 5,155	$ 19,995	$ 11,972
2018 RPI Funding Agreement
Liability For Sale Of Future Royalties [Roll Forward]
Liability related to sale of future royalties - beginning balance			144,111	117,515
Royalty revenues payable to RPI			(228)	0
Non-cash interest expense on liability related to sale of future royalties			19,995	11,972
Liability related to sale of future royalties - ending balance	$ 163,878	$ 129,487	$ 163,878	$ 129,487