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Share-Based Compensation - Schedule of Estimated Fair Value of Share-Based Awards on Respective Grant Dates using Binomial Option Pricing Model (Detail) (USD $)
0 Months Ended 9 Months Ended
Oct. 22, 2013
May 27, 2013
Jul. 01, 2012
Dec. 19, 2011
Oct. 08, 2011
Aug. 01, 2011
May 06, 2011
Sep. 30, 2014
Dec. 31, 2013
Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                    
Fair value of ordinary share $ 11.64 $ 4.58 $ 3.70 $ 3.68 $ 3.68 $ 3.44 $ 3.69 $ 3.76 $ 2.65 $ 2.38
Risk-free interest rates 2.60% 2.07% 1.73% 1.89% 2.14% 2.90% 3.27%      
Expected exercise multiple $ 2.2 $ 2.2 $ 2.2 $ 2.2 $ 2.2 $ 2.2 $ 2.2      
Expected volatility 53.70% 55.49% 60.40% 60.80% 60.70% 60.50% 61.90%      
Expected dividend yield 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%      
Weighted average fair value per option granted   $ 3.03 $ 2.36 $ 2.41 $ 2.37 $ 2.18 $ 2.40 $ 34.57    
Minimum [Member]
                   
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                    
Weighted average fair value per option granted $ 9.63                  
Maximum [Member]
                   
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                    
Weighted average fair value per option granted $ 9.69