License and Collaboration Agreements - Additional Information (Detail) - Development and Commercialization Milestones [Member] - Asset Sale Agreement [Member] - USD ($)		12 Months Ended
	Apr. 03, 2017	Dec. 31, 2018
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Maximum amount of milestone payments that can be received		$ 33,000,000
Milestone payment received		28,000,000
Ipsen [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Maximum amount of milestone payments that can be received	$ 33,000,000
Milestone payment received		$ 28,000,000