Liability Related to Sale of Future Royalties, net - Activity within Liability Account (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Liability related to sales of future royalties
Interest expense on liability related to sale of future royalties	$ 13,508	$ 8,425
2018 and 2020 RPI Funding Agreements
Liability related to sales of future royalties
Liability related to sale of future royalties - beginning balance	335,282	144,111
Royalty revenues payable to RPI	(1,096)	(24)
Interest expense on liability related to sale of future royalties	13,508	8,425
Liability related to sale of future royalties - ending balance	$ 347,694	$ 152,512