Liability Related to Sale of Future Royalties - Additional Information (Detail) - USD ($) $ in Thousands		3 Months Ended				6 Months Ended		70 Months Ended
	Feb. 24, 2012	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2017
Liability Related to Sale of Future Royalties [Line Items]
Non-cash royalty revenue related to sale of future royalties						$ 17,321	$ 15,965
Non-cash interest expense on liability related to sale of future royalties		$ (5,975)		$ (4,975)		$ (12,040)	$ (9,994)
Annual interest rate			18.70%		17.60%			17.00%
Prospective interest rate			29.00%		21.00%
Purchase and Sale Agreement with RPI
Liability Related to Sale of Future Royalties [Line Items]
Proceeds from sale of royalty rights	$ 124,000
Transaction costs related to sale of potential future royalties	$ 4,400