Strategic Alliances and Collaborations - Additional Information (Detail)	1 Months Ended													2 Months Ended	6 Months Ended	8 Months Ended	12 Months Ended
	Dec. 31, 2015 USD ($) shares	Sep. 30, 2015 USD ($)	Jul. 31, 2015	May. 31, 2015 USD ($)	Mar. 31, 2015 USD ($)	Jan. 31, 2015 USD ($)	Oct. 31, 2014 USD ($)	Aug. 31, 2014 USD ($)	Feb. 28, 2014 USD ($) $ / shares shares	Jul. 31, 2013 USD ($)	Jun. 30, 2013 USD ($)	Oct. 31, 2012 USD ($) $ / shares shares	Aug. 31, 2012 USD ($) agreement	Nov. 30, 2013 USD ($)	Jun. 30, 2015	Jan. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) shares	Dec. 31, 2014 USD ($) shares
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Common stock value	$ 53,000																$ 53,000	$ 49,000
Common stock, shares issued | shares	52,669,266																52,669,266	48,944,530
AstraZeneca
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of collaborative areas granted | agreement													3
Initial upfront option payment												$ 3,000,000
Expected term of research and development plan												4 years
Common stock value													$ 25,000,000
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
Restricting common stock valuation measurement period												1 year
Upfront Payment Received												$ 4,300,000
Deferred revenue remaining recognition period (less than)																	1 year
Expected revenue through milestone payments					$ 485,500,000
AstraZeneca | Minimum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalties based on percentage of net sales					10.00%
AstraZeneca | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalties based on percentage of net sales					20.00%
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]
Expected revenue through milestone payments					113,000,000
Milestone payments, earned	$ 10,000,000
AstraZeneca | Commercialization
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expected revenue through milestone payments					$ 370,000,000
AstraZeneca | Side Letter
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognized																	$ 4,500,000
AstraZeneca | Side Letter | Pre-IND and API manufacturing activities
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of cost funded						50.00%
AstraZeneca | Side Letter | Phase I clinical study product manufacturing activities
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of cost funded						100.00%
AstraZeneca | Common Stock Purchase Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue	1,100,000																1,100,000
Sanofi
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront Payment Received									$ 400,000
Deferred revenue									400,000
Sanofi | Private Placement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Common stock value									$ 10,000,000
Common stock, shares issued | shares									1,303,780
Price per share (in dollars per share) | $ / shares									$ 7.67
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									$ 2,500,000	$ 2,500,000
Deferred Revenue Creditable Against Future Milestones																	$ 1,250,000
Upfront payment creditable against future accounts receivables									$ 1,250,000	$ 1,250,000
Upfront payment non-creditable portion recognized																$ 1,250,000
Sanofi | Research and development
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Initial upfront option payment																25,000,000
Deferred revenue																$ 10,100,000
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	15,000,000																$ 15,000,000
Sanofi | Common Stock Purchase Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue	300,000																$ 300,000
Deferred revenue remaining recognition period (less than)																	4 years
Sanofi | Proof-of-Concept Trial
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expected revenue through milestone payments	101,800,000																$ 101,800,000
Sanofi | Regulatory and Commercialization Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expected revenue through milestone payments	$ 300,000,000																$ 300,000,000
GSK
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue recognition period																	8 years
Acceleration of remaining amortization of upfront payment							$ 3,100,000				$ 1,100,000
Biogen
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Initial upfront option payment								$ 2,000,000					800,000
Deferred revenue		$ 0
Deferred revenue remaining recognition period (less than)			14 months												12 months
Revenue recognized													$ 800,000
Acceleration of remaining amortization of upfront payment								$ 100,000
Revenue recognition period								1 year					2 years
Biogen | Research and development
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments, earned		$ 300,000		$ 300,000		$ 100,000
Revenue recognized								$ 2,000,000
Biogen | Research Tax Credit Carryforward
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expected revenue through milestone payments													$ 1,300,000
Biogen | Amended Collaboration and License Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments, earned														$ 300,000