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, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Liability Related to Sale of Future Royalties [Line Items]
Non-cash royalty revenue related to sale of future royalties				$ 15,965	$ 13,301
Non-cash interest expense on liability related to sale of future royalties		$ 4,975	$ 4,512	$ 9,994	$ 9,064
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