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Strategic Alliances and Collaborations (Detail)	1 Months Ended			3 Months Ended		6 Months Ended		8 Months Ended
Strategic Alliances and Collaborations (Detail)	Feb. 28, 2014 USD ($) $ / shares shares	Jul. 31, 2013 USD ($)	Jul. 31, 2012 target	Jun. 30, 2018 USD ($) shares	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) shares	Jun. 30, 2017 USD ($)	Jan. 31, 2014 USD ($)	Jan. 01, 2018 USD ($)	Dec. 31, 2017 USD ($) shares
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenues (less than)				$ 18,000	$ 18,000	$ 36,000	$ 36,000
Common stock, shares issued \| shares				104,424,492		104,424,492				103,955,147
Common stock value				$ 104,000		$ 104,000				$ 104,000
Deferred revenue									$ 77,000
Revenue under strategic alliances and collaborations
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenues (less than)				100,000	$ 100,000	$ 100,000	$ 100,000
Sanofi
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of collaborative areas granted \| target			4
Deferred revenue	$ 400,000
Sanofi \| Private Placement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Common stock, shares issued \| shares	1,303,780
Price per share (in dollars per share) \| $ / shares	$ 7.67
Common stock value	$ 10,000,000
Restriction period in which Alliances could not sell, transfer, make any short sale of, or grant any option for the sale of any common stock	12 months
Sanofi \| Minimum \| United States
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalties based on percentage of net sales						10.00%
Sanofi \| Minimum \| Outside of the United States
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalties based on percentage of net sales						10.00%
Sanofi \| Maximum \| United States
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalties based on percentage of net sales						20.00%
Sanofi \| Maximum \| Outside of the United States
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalties based on percentage of net sales						20.00%
Sanofi \| Development Commercialization And License Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Initial upfront option payment		$ 2,500,000
Deferred revenue creditable against future milestones	$ 1,250,000	$ 1,250,000				$ 1,250,000
Upfront payment non-creditable portion recognized								$ 1,250,000
Sanofi \| Common Stock Purchase Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue				100,000		$ 100,000
Deferred revenue recognition period						2 years
Sanofi \| Proof-of-Concept Trial
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential revenue through milestone payments				101,800,000.0		$ 101,800,000.0
Sanofi \| Regulatory and Commercialization Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential revenue through milestone payments				300,000,000.0		300,000,000.0
Sanofi \| Clinical
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential revenue through milestone payments				$ 15,000,000.0		$ 15,000,000.0