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Net Loss Per Share - Additional Information (Detail)
3 Months Ended 9 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Sep. 30, 2013
Sep. 30, 2012
Earnings Per Share [Abstract]        
Weighted-average shares subject to repurchase from the weighted-average number of common shares outstanding 101,875 116,875 105,625 120,625