Quarterly report pursuant to Section 13 or 15(d)

Common Stock - Summary of Stock Option Activity (Detail)

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Common Stock - Summary of Stock Option Activity (Detail) (USD $)
In Thousands, except Share data, unless otherwise specified
 6 Months Ended 12 Months Ended
Jun. 30, 2013
Dec. 31, 2012
Summary of stock option activity    
Number of Shares, Beginning of period 2,519,070  
Number of Shares, Options granted 2,031,590  
Number of Shares, Options exercised (245,157)  
Number of Shares, Options cancelled (20,000)  
Number of Shares, End of period 4,285,503 2,519,070
Number of Shares, Options vested and expected to vest 4,285,503  
Number of Shares, Options vested and exercisable 1,047,053  
Weighted Average Exercise Price, Beginning of period $ 3.37  
Weighted Average Exercise Price, Options granted $ 6.07  
Weighted Average Exercise Price, Options exercised $ 1.56  
Weighted Average Exercise Price, Options cancelled $ 1.93  
Weighted Average Exercise Price, End of period $ 4.77 $ 3.37
Weighted Average Exercise Price, Options vested and expected to vest $ 4.77  
Weighted Average Exercise Price, Options vested and exercisable $ 2.84  
Total Weighted Average Intrinsic Value, Beginning of period $ 2,860  
Total Weighted Average Intrinsic Value, End of period 16,434 2,860
Total Weighted Average Intrinsic Value, Options vested and expected to vest 16,434  
Total Weighted Average Intrinsic Value, Options vested and exercisable $ 6,031  
Weighted Average Remaining Contractual Life 8 years 10 months 24 days 8 years 6 months
Weighted Average Remaining Contractual Life, Options vested and expected to vest 8 years 10 months 24 days  
Weighted Average Remaining Contractual Life, Options vested and exercisable 7 years 10 months 24 days