Liability Related to the Sale of Future Royalties and Milestones (Schedule of Liability Account) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)
Liability related to sale of future royalties and milestones - beginning balance	$ 210,795
Non-cash royalty revenue	(30,424)
Non-cash interest expense recognized	41,474
Liability related to sale of future royalties and milestones - ending balance	221,845
Less: unamortized transaction costs	(476)
Liability related to sale of future royalties and milestones, net	221,369
Period from Inception [Member]
Proceeds from sale of future royalties and milestones	205,000
Non-cash royalty revenue	(47,733)
Non-cash interest expense recognized	64,578
Liability related to sale of future royalties and milestones - ending balance	221,845
Less: unamortized transaction costs	(476)
Liability related to sale of future royalties and milestones, net	$ 221,369