Quarterly report pursuant to Section 13 or 15(d)

Organization and Description of Business - Additional Information (Detail)

v2.4.0.8
Organization and Description of Business - Additional Information (Detail) (USD $)
In Thousands, except Share data, unless otherwise specified
 9 Months Ended 87 Months Ended 9 Months Ended 0 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Sep. 30, 2013
Dec. 31, 2012
Sep. 30, 2013
2012 and 2013 ATMs [Member]
Oct. 02, 2013
Subsequent Event [Member]
2013 ATM [Member]
Organization And Nature Of Business [Line Items]            
Accumulated deficit $ (111,544)   $ (111,544) $ (84,184)    
Public offering of common stock, shares         10,352,219 206,203
Net proceeds from public offering of common stock $ 90,629 $ 28,750 $ 119,682   $ 88,000 $ 1,400