Liabilities Related to the Sales of Future Royalties - Summary of Liability Related to Potential Future Royalties (Detail) - USD ($) $ in Thousands		12 Months Ended			106 Months Ended
	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020
Liability Related to the Sale of Future Royalties [Line Items]
Liability related to the sale of future royalties—beginning balance		$ 73,551			$ 0
Royalty monetization proceeds		150,000			274,000
Non-cash royalty revenue		48,563	$ 36,303	$ 33,308	255,705
Non-cash interest expense		30,267	25,044	$ 21,196	196,960
Payments to RPI		0			(10,000)
Liability related to the sale of future royalties – ending balance	$ 205,255	205,255	73,551		205,255
Less: unamortized transaction costs	(4,915)	(4,915)			(4,915)
Liability related to the sale of future royalties, net	200,340	200,340	72,020		200,340
Purchase and Sale Agreement 2012
Liability Related to the Sale of Future Royalties [Line Items]
Liability related to the sale of future royalties—beginning balance		73,551			0
Royalty monetization proceeds		0			124,000
Non-cash royalty revenue		37,938			245,080
Non-cash interest expense		30,267			196,960
Payments to RPI		0			(10,000)
Liability related to the sale of future royalties – ending balance	65,880	65,880	$ 73,551		65,880
Less: unamortized transaction costs	(1,165)	(1,165)			(1,165)
Liability related to the sale of future royalties, net	64,715	$ 64,715			64,715
Implicit interest rate over the life of the agreement		20.20%	19.50%	18.70%
Prospective effective interest rate		48.00%	38.00%	29.00%
Purchase and Sale Agreement 2020
Liability Related to the Sale of Future Royalties [Line Items]
Liability related to the sale of future royalties—beginning balance	0	$ 0
Royalty monetization proceeds	150,000	150,000
Non-cash royalty revenue	10,625	10,625
Non-cash interest expense	0	0
Payments to RPI	0	0
Liability related to the sale of future royalties – ending balance	139,375	139,375	$ 0		139,375
Less: unamortized transaction costs	(3,750)	(3,750)			(3,750)
Liability related to the sale of future royalties, net	$ 135,625	$ 135,625			$ 135,625
Implicit interest rate over the life of the agreement				16.00%
Prospective effective interest rate				16.00%