Liability Related to Sale of Future Royalties, net - Activity within Liability Account (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Liability For Sale Of Future Royalties [Roll Forward]
Non-cash interest expense on liability related to sale of future royalties	$ 11,955	$ 7,312	$ 31,950	$ 19,284
2018 and 2020 RPI Funding Agreements
Liability For Sale Of Future Royalties [Roll Forward]
Liability related to sale of future royalties - beginning balance			144,111	117,515
Additional liability related to the 2020 RPI Funding Agreement, net of issuance costs			147,476	0
Royalty revenues payable to RPI			(667)	0
Non-cash interest expense on liability related to sale of future royalties			31,950	19,284
Liability related to sale of future royalties - ending balance	$ 322,870	$ 136,799	$ 322,870	$ 136,799