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
 6 Months Ended 84 Months Ended 6 Months Ended 1 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Jun. 30, 2013
Dec. 31, 2012
Jun. 30, 2013
2012 and 2013 ATMs [Member]
Aug. 02, 2013
Subsequent Event [Member]
2013 ATM [Member]
Organization And Nature Of Business [Line Items]            
Accumulated deficit $ (103,712)   $ (103,712) $ (84,184)    
Public offering of Common Stock, shares         4,864,757 2,200,000
Net proceeds from public offering of Common Stock $ 44,240 $ 28,750 $ 73,293   $ 42,800 $ 18,400