Summary of Significant Accounting Policies - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014 Candidate	Dec. 31, 2013	Jun. 30, 2013	Dec. 31, 2012
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Number of VDA drug candidates tested	2
Accumulated earnings (deficit)	$ (245,067)	$ (238,508)
Cash	$ 36,271	$ 7,005	$ 7,732	$ 4,946