Basis of Presentation and Summary of Significant Accounting Policies - Royalty Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Total revenues	$ 27,003	$ 24,808	$ 24,987	$ 43,484	$ 59,590	$ 45,663	$ 90,043	$ 56,157	$ 120,282	$ 251,453	$ 141,102
Royalties
Disaggregation of Revenue [Line Items]
Total revenues									46,976	128,556	88,685
Royalty, Promacta
Disaggregation of Revenue [Line Items]
Total revenues									14,193	99,260
Royalty, Kyprolis
Disaggregation of Revenue [Line Items]
Total revenues									25,046	21,686
Royalty, Evomela
Disaggregation of Revenue [Line Items]
Total revenues									5,171	5,658
Royalty, Other
Disaggregation of Revenue [Line Items]
Total revenues									$ 2,566	$ 1,952
Calculated under Revenue Guidance in Effect before Topic 606 | Royalty, Promacta
Disaggregation of Revenue [Line Items]
Total revenues											62,918
Calculated under Revenue Guidance in Effect before Topic 606 | Royalty, Kyprolis
Disaggregation of Revenue [Line Items]
Total revenues											16,413
Calculated under Revenue Guidance in Effect before Topic 606 | Royalty, Evomela
Disaggregation of Revenue [Line Items]
Total revenues											7,155
Calculated under Revenue Guidance in Effect before Topic 606 | Royalty, Other
Disaggregation of Revenue [Line Items]
Total revenues											$ 2,199