Summary of Significant Accounting Policies - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014 Candidate	Dec. 31, 2013	Sep. 30, 2013	Dec. 31, 2012
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of VDA drug candidates tested	2
Accumulated earnings (deficit)	$ (248,517)	$ (238,508)
Cash	$ 32,887	$ 7,005	$ 8,777	$ 4,946