Quarterly report pursuant to Section 13 or 15(d)

Net Loss Per Common Share - Calculation of Basic and Diluted Net Loss Per Share (Detail)

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Net Loss Per Common Share - Calculation of Basic and Diluted Net Loss Per Share (Detail) (USD $)
In Thousands, except Share data, unless otherwise specified
3 Months Ended 9 Months Ended 87 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Sep. 30, 2013
Sep. 30, 2012
Sep. 30, 2013
Numerator:          
Net loss attributed to common stockholders $ (7,832) $ (5,935) $ (27,360) $ (18,945) $ (117,405)
Denominator:          
Weighted-average common shares outstanding-denominator for basic and diluted net loss per share 32,634,683 24,375,749 28,664,822 20,738,007  
Basic and diluted net loss per common share attributed to common stockholders $ (0.24) $ (0.24) $ (0.95) $ (0.91)