Quarterly report pursuant to Section 13 or 15(d)

Stock Based Compensation - Stock Option Activity Under Equity Incentive Plan (Detail)

v2.4.0.6
Stock Based Compensation - Stock Option Activity Under Equity Incentive Plan (Detail) (USD $)
 3 Months Ended
Mar. 31, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]  
Number of Shares, Outstanding at December 31, 2012 5,098,972
Number of Shares, Granted 1,448,500
Number of Shares, Exercised (25,423)
Number of Shares, Forfeitures (41,458)
Number of Shares, Outstanding at March 31, 2013 6,480,591
Number of Shares, Vested and expected to vest March 31, 2013 6,396,070
Number of Shares, Exercisable at March 31, 2013 2,634,337
Weighted-Average Exercise Price, Outstanding at December 31, 2012 $ 3.18
Weighted-Average Exercise Price, Granted $ 5.05
Weighted-Average Exercise Price, Exercised $ 1.29
Weighted-Average Exercise Price, Forfeitures $ 7.69
Weighted-Average Exercise Price, Outstanding at March 31, 2013 $ 3.58
Weighted-Average Exercise Price, Vested and expected to vest March 31, 2013 $ 3.56
Weighted-Average Exercise Price, Exercisable at March 31, 2013 $ 2.15
Weighted-Average Remaining Contractual Term, Outstanding at March 31, 2013 8 years 3 months 4 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest March 31, 2013 8 years 2 months 27 days
Weighted-Average Remaining Contractual Term, Exercisable at March 31, 2013 7 years 1 month 6 days
Aggregate Intrinsic Value, Outstanding at March 31, 2013 $ 10,700,852
Aggregate Intrinsic Value, Vested and expected to vest March 31, 2013 10,668,639
Aggregate Intrinsic Value, Exercisable at March 31, 2013 $ 7,190,145