Liability Related to Sale of Future Royalties (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended		70 Months Ended
	Feb. 24, 2012	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2017
Liability Related to Sale of Future Royalties [Line Items]
Non-cash royalty revenue related to sale of future royalties				$ 28,001	$ 27,585
Non-cash interest expense on liability related to sale of future royalties		$ (8,425)	$ (5,813)	$ (22,084)	$ (17,853)
Annual interest rate		20.20%				17.00%
Prospective interest rate		48.00%
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