Liability Related to the Sale of Future Royalties - Summary of Liability Related to Potential Future Royalties (Detail) - USD ($) $ in Thousands	12 Months Ended			82 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018
Other Liabilities Disclosure [Abstract]
Liability related to the sale of future royalties—beginning balance	$ 96,922			$ 0
Proceeds from sale of future royalties	0			124,000
Payments from Nektar to RPI	0			(10,000)
Non-cash CIMZIA® and MIRCERA® royalty revenue	(33,308)	$ (30,531)	$ (30,158)	(170,839)
Non-cash interest expense recognized	21,196	18,869	$ 19,712	141,649
Liability related to the sale of future royalties – ending balance	84,810	96,922		84,810
Less: unamortized transaction costs	(1,899)			(1,899)
Liability related to the sale of future royalties, net	$ 82,911	$ 94,655		$ 82,911