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 $)
 6 Months Ended
Jun. 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 1,618,500
Number of Shares, Exercised (95,825)
Number of Shares, Forfeitures (51,458)
Number of Shares, Outstanding at June 30, 2013 6,570,189
Number of Shares, Vested and expected to vest June 30, 2013 6,500,552
Number of Shares, Exercisable at June 30, 2013 2,977,250
Weighted-Average Exercise Price, Outstanding at December 31, 2012 $ 3.18
Weighted-Average Exercise Price, Granted $ 5.10
Weighted-Average Exercise Price, Exercised $ 1.76
Weighted-Average Exercise Price, Forfeitures $ 7.71
Weighted-Average Exercise Price, Outstanding at June 30, 2013 $ 3.64
Weighted-Average Exercise Price, Vested and expected to vest June 30, 2013 $ 3.62
Weighted-Average Exercise Price, Exercisable at June 30, 2013 $ 2.44
Weighted-Average Remaining Contractual Term, Outstanding at June 30, 2013 8 years 26 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest June 30, 2013 8 years 22 days
Weighted-Average Remaining Contractual Term, Exercisable at June 30, 2013 7 years 29 days
Aggregate Intrinsic Value, Outstanding at June 30, 2013 $ 13,093,522
Aggregate Intrinsic Value, Vested and expected to vest June 30, 2013 13,056,277
Aggregate Intrinsic Value, Exercisable at June 30, 2013 $ 9,109,942