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, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2017
Liability Related to Sale of Future Royalties [Line Items]
Non-cash royalty revenue related to sale of future royalties							$ (17,579)	$ (17,321)
Non-cash interest expense on liability related to sale of future royalties		$ (6,691)		$ (5,975)			$ (13,659)	$ (12,040)
Annual interest rate			19.50%		18.70%	17.60%			17.00%
Prospective interest rate			38.00%		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