Collaboration Agreements - Additional Information (Detail) (USD $)	1 Months Ended		3 Months Ended		6 Months Ended					6 Months Ended
	Oct. 31, 2011	Apr. 30, 2010	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 Candidate Licensed_Program Vendor	Jun. 30, 2012	Jun. 30, 2013 Maximum [Member]	Oct. 31, 2011 Maximum [Member]	Jun. 30, 2013 Minimum [Member]	Jun. 30, 2013 Series B Preferred Stock [Member]	Dec. 31, 2012 Series B Preferred Stock [Member]
Collaboration Agreements [Line Items]
Amended collaboration expiration date		2014-04
Discovery phase years		2 years
Number of candidates confirmed by the Joint Research Committee					2
Company entitled to receive milestone payment			$ 5,000,000		$ 5,000,000
Number of licensed programs type under collaboration agreements					3
Period considered for agreement termination notice					90 days
Company received upfront payment					121,200,000
Series B convertible preferred stock, purchased										5,190,551	5,190,551
Series B convertible preferred stock Price per share										$ 1.70
Net Proceeds of Series B convertible preferred stock										8,800,000
Additional consideration under agreement										3,100,000
Series B Preferred Stock was recorded at its fair value										5,681,000	5,681,000
Number of vendors selling similar competitive products					0
Company expects to fulfill its performance obligations					124,300,000
Number of years company expected to fulfill its performance obligations					6 years
Agreement was amended to extend the term of the initial discovery period	3 years
Agreement was amended to extend the term of the initial discovery period	4 years
Payment made in pursuant to the amendment	20,000,000
Company eligible to receive in extension payment								40,000,000
Date of Extension of discovery phase	2016-04
Revenue			6,268,000	6,288,000	12,536,000	12,556,000
Receipts of Potential milestone payments							120,000,000
Milestone payment upon achievement of a specified clinical development milestone event							25,000,000
Milestone payments upon achievement of specified regulatory milestone events							70,000,000
Milestone payment upon achievement of a specified commercial milestone event							25,000,000
Achievement of an early clinical development milestone event			22,500,000		22,500,000
Dosing of the last patient in a Company-sponsored			25,000,000		25,000,000
Potential milestone that the Company might be entitled to receive enrollment of the last patient									$ 5,000,000