License and Collaboration Agreements - Additional Information (Detail) - Ipsen [Member] - Asset Sale Agreement [Member]	Apr. 03, 2017 USD ($)
Development and Commercialization Milestones [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Maximum amount of milestone payments that can be received	$ 33,000,000
Sale Milestones in Major European Countries [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential milestone payments receivable	18,000,000
Sale Milestones in Major Non-European and Non-Asian Country [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential milestone payments receivable	5,000,000
Clinical Trials in Lung Cancer [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential milestone payments receivable	$ 10,000,000