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Shared-Based Payments - Schedule of Stock Option Activity (Detail) (USD $)
 9 Months Ended 12 Months Ended
Sep. 30, 2013
Dec. 31, 2012
Dec. 31, 2011
Mar. 16, 2011
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]        
Number of Options, Outstanding, Beginning Balance 3,249,702 2,885,417    
Number of Options, Granted 687,183 454,014    
Number of Options, Exercised (1,025,933) (49,883)    
Number of Options, Forfeited or expired (33,949) (39,846)    
Number of Options, Outstanding, Ending Balance 2,877,003 3,249,702 2,885,417  
Weighted- Average Exercise Price, Outstanding, Beginning Balance $ 0.94 $ 0.94   $ 0.94
Number of Options, Exercisable 1,855,178 2,620,100    
Weighted- Average Exercise Price, Granted $ 3.19 $ 0.94    
Number of Options, Vested and expected to vest 918,600 2,734,949    
Weighted- Average Exercise Price, Exercised $ 0.75 $ 0.94    
Weighted- Average Exercise Price, Forfeited or expired $ 1.13 $ 0.94    
Weighted- Average Exercise Price, Outstanding, Ending Balance $ 1.50 $ 0.94 $ 0.94 $ 0.94
Weighted- Average Exercise Price, Exercisable $ 0.94 $ 0.94    
Weighted- Average Exercise Price, Vested and expected to vest $ 2.44 $ 0.94    
Weighted Average Contractual Term, Granted 7 years 6 years 8 months 12 days    
Weighted Average Contractual Term, Outstanding 7 years 2 months 12 days 7 years 3 months 18 days 7 years 4 months 24 days