Strategic Alliances and Collaborations (Detail)	1 Months Ended							8 Months Ended	9 Months Ended
	Dec. 31, 2015 USD ($)	Mar. 31, 2015 USD ($)	Feb. 28, 2014 USD ($) $ / shares shares	Jul. 31, 2013 USD ($)	Oct. 31, 2012 USD ($) $ / shares shares	Aug. 31, 2012 target	Jul. 31, 2012 target	Jan. 31, 2014 USD ($)	Sep. 30, 2017 USD ($) shares	Dec. 31, 2016 USD ($) shares
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Common stock, shares issued | shares									103,955,147	52,924,805
Common stock value									$ 104,000	$ 53,000
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									$ 200,000
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
Sanofi | Regulatory and Commercialization Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential revenue through milestone payments									300,000,000.0
Sanofi | Clinical
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential revenue through milestone payments									$ 15,000,000.0
AstraZeneca
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of collaborative areas granted | target						3
Initial upfront option payment					$ 3,000,000
Common stock, shares issued | shares					6,250,000
Price per share (in dollars per share) | $ / shares					$ 4.00
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					365 days
Deferred revenue					$ 4,300,000
Expected term of research and development plan (years)					4 years
AstraZeneca | Preclinical
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments, earned		$ 2,500,000
AstraZeneca | Clinical
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments, earned	$ 10,000,000