Revenue Recognition - Additional Information (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2017 USD ($)
Clinical Development
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Potential milestone payments to be received	$ 60
Milestone payment substantive	60
Initial Commercial Sales
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Potential milestone payments to be received	100
BioMarin Pharmaceutical, Inc. | Asset Purchase Agreement
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Potential milestone payments to be received	$ 160