Liability Related to Sale of Future Royalties - Additional Information (Detail) - USD ($) $ in Thousands		3 Months Ended		70 Months Ended
	Feb. 24, 2012	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Liability Related to Sale of Future Royalties [Line Items]
Non-cash royalty revenue related to sale of future royalties		$ 6,920	$ 6,663
Non-cash interest expense on liability related to sale of future royalties		$ 5,019	$ 4,552
Annual interest rate		17.60%		17.00%
Prospective interest rate		21.00%
Purchase and Sale Agreement with RPI [Member]
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