Quarterly report pursuant to Section 13 or 15(d)

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

v2.4.0.8
Stock Based Compensation - Stock Option Activity Under Equity Incentive Plan (Detail) (USD $)
 9 Months Ended
Sep. 30, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]  
Number of Shares, Outstanding at December 31, 2012 5,098,972
Number of Shares, Granted 1,653,500
Number of Shares, Exercised (127,153)
Number of Shares, Forfeitures (65,303)
Number of Shares, Outstanding at September 30, 2013 6,560,016
Number of Shares, Vested and expected to vest September 30, 2013 6,504,707
Number of Shares, Exercisable at September 30, 2013 3,361,581
Weighted-Average Exercise Price, Outstanding at December 31, 2012 $ 3.18
Weighted-Average Exercise Price, Granted $ 5.10
Weighted-Average Exercise Price, Exercised $ 1.59
Weighted-Average Exercise Price, Forfeitures $ 7.15
Weighted-Average Exercise Price, Outstanding at September 30, 2013 $ 3.66
Weighted-Average Exercise Price, Vested and expected to vest September 30, 2013 $ 3.64
Weighted-Average Exercise Price, Exercisable at September 30, 2013 $ 2.67
Weighted-Average Remaining Contractual Term, Outstanding at September 30, 2013 7 years 9 months 29 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest September 30, 2013 7 years 9 months 26 days
Weighted-Average Remaining Contractual Term, Exercisable at September 30, 2013 7 years 4 days
Aggregate Intrinsic Value, Outstanding at September 30, 2013 $ 10,534,778
Aggregate Intrinsic Value, Vested and expected to vest September 30, 2013 10,518,742
Aggregate Intrinsic Value, Exercisable at September 30, 2013 $ 8,034,963