Liability Related to the Sale of Future Royalties - Summary of Liability Related to Potential Future Royalties (Detail) - USD ($) $ in Thousands	12 Months Ended			94 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019
Liability Related To The Sale Of Future Royalties [Roll Forward]
Liability related to the sale of future royalties—beginning balance	$ 84,810			$ 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	(36,303)	$ (33,308)	$ (30,531)	(207,142)
Non-cash interest expense recognized	25,044	21,196	$ 18,869	166,693
Liability related to the sale of future royalties – ending balance	73,551	84,810		73,551
Less: unamortized transaction costs	(1,531)			(1,531)
Liability related to the sale of future royalties, net	$ 72,020	$ 82,911		$ 72,020