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Research Collaboration and License Agreement - Additional Information (Detail) - Research Collaboration and License Agreement [Member] - PTG-300 [Member] - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Mar. 31, 2017	Sep. 30, 2017
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment based on agreement		$ 250,000
Milestone payment upon contractual obligation	$ 250,000
Term (in years)			10 years
Development Milestones [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Aggregate milestone payment			$ 28,500,000.0
Sales Milestones [Member] | Maximum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Aggregate milestone payment			$ 100,000,000.0

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