Convertible Notes Payable - Additional Information (Detail) (USD $)	1 Months Ended				12 Months Ended			1 Months Ended
	Aug. 31, 2012	Jul. 31, 2012	Feb. 28, 2010	Apr. 30, 2008	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Oct. 31, 2012
Debt Instrument [Line Items]
Term of convertible note payable				3 years
Proceeds from issuance of convertible notes payable			$ 5,000,000	$ 5,000,000
Convertible notes amendment date					2012-07
Conversion of convertible notes, converted number of common stock	1,256,232
Conversion price per shares	$ 4.00
Loss on extinguishment of debt		(1,700,000)					(1,738,000)
Convertible note payable, at fair value, noncurrent						11,279,000
Convertible note payable, at fair value, current					23,397,000
Loss from change in value of convertible note payable					(12,118,000)	(1,145,000)	(2,969,000)
Issued promissory note	5,000,000
April 2008
Debt Instrument [Line Items]
Voting securities percentage					50.00%
Convertible notes payable								5,000,000
Conversion price per shares								4.00
April 2008 | Common Stock
Debt Instrument [Line Items]
Conversion of convertible notes, converted number of common stock								1,447,037
October 2012
Debt Instrument [Line Items]
Conversion price per shares								4.00
Outstanding principal amount								5,000,000
Accrued interest on convertible notes								400,000
Maturity period of note								3 years
Conversion date								2015-10
October 2012 | Convertible Debt | GSK
Debt Instrument [Line Items]
Convertible notes issued								5,400,000