Strategic Alliances and Collaborations (Details) $ / shares in Units, $ in Thousands	1 Months Ended												8 Months Ended	12 Months Ended
	Jul. 31, 2017 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	May 31, 2015 USD ($)	Mar. 31, 2015 USD ($)	Jan. 31, 2015 USD ($)	Aug. 31, 2014 USD ($)	Feb. 28, 2014 USD ($) $ / shares shares	Jul. 31, 2013 USD ($)	Oct. 31, 2012 USD ($) $ / shares shares	Aug. 31, 2012 agreement	Jul. 31, 2010 target	Jan. 31, 2014 USD ($)	Dec. 31, 2017 USD ($) 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	$ 53
Sanofi
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of collaborative areas granted | target												4
Upfront payment received								$ 400
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
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 | Development Commercialization And License Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Initial upfront option payment								$ 2,500	$ 2,500
Upfront payment non-creditable portion recognized													$ 1,250
Deferred revenue creditable against future milestones	$ 1,250							$ 1,250						$ 1,250
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 US
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 US
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalties based on percentage of net sales														20.00%
Sanofi | Clinical
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expected revenue through milestone payments														$ 15,000
Sanofi | Common Stock Purchase Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue														$ 100
Deferred revenue recognition period														2 years
Sanofi | Proof-of-Concept Trial
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expected revenue through milestone payments														$ 101,800
Sanofi | Regulatory and Commercialization Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expected revenue through milestone payments														$ 300,000
AstraZeneca
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of collaborative areas granted | agreement											3
Initial upfront option payment										$ 3,000
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
Upfront payment received										$ 4,300
Expected term of research and development plan										4 years
AstraZeneca | Preclinical
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments, earned					$ 2,500
AstraZeneca | Clinical
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments, earned		$ 10,000
Biogen
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Initial upfront option payment							$ 2,000
Biogen | Research and development
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments, earned			$ 300	$ 300		$ 100