Collaboration Agreements - Additional Information (Detail) (USD $)	3 Months Ended	9 Months Ended				1 Months Ended	9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 Sanofi Aventis	Sep. 30, 2012 Sanofi Aventis	Mar. 16, 2013 Takeda Pharmaceutical Company Limited	Sep. 30, 2012 Takeda Pharmaceutical Company Limited	Sep. 30, 2012 Takeda Pharmaceutical Company Limited Research and Development Funding	Sep. 30, 2013 Pfizer	Sep. 30, 2012 Pfizer	Sep. 30, 2013 Pfizer	Sep. 30, 2012 Pfizer
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract revenue	$ 2,913,000	$ 0	$ 3,037,000	$ 0	$ 2,900,000			$ 100,000	$ 0	$ 0	$ 0	$ 0
Reimbursement of research costs						$ 0	$ 100,000		$ 0	$ 0	$ 0	$ 0