Collaboration Agreement - Additional Information (Detail) - Bayer Healthcare LLC [Member] - Collaboration Agreement [Member] - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended
	Jun. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront license payment received	$ 20,000,000
Research agreement period	54 months
Research agreement commencement date	2014-06
Research payments earned		$ 2,092,000	$ 1,290,000	$ 5,470,000	$ 1,290,000
Deferred revenue		$ 22,715,000		$ 22,715,000
Maximum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential future milestone payments receivable under development and commercialization activities	$ 232,000,000