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Share-Based Compensation - Additional Information (Detail) (USD $)
 1 Months Ended 12 Months Ended 1 Months Ended 12 Months Ended 1 Months Ended 12 Months Ended 12 Months Ended
Nov. 30, 2012
Sep. 30, 2007
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Nov. 30, 2012
Shares Vesting in May Twenty Thirteen
Nov. 30, 2012
Shares Vesting in November Twenty Thirteen
Dec. 31, 2012
Conversion of Options to restricted shares
After Modification
Dec. 31, 2012
Conversion of Options to restricted shares
Before Modification
Dec. 31, 2012
Stock Options
Dec. 31, 2011
Stock Options
Dec. 31, 2010
Stock Options
Dec. 31, 2012
Stock Options
Modification of Exercise Price
After Modification
Dec. 31, 2012
Stock Options
Modification of Exercise Price
After Modification
American Depositary Share
Dec. 31, 2012
Stock Options
Modification of Exercise Price
Before Modification
Jun. 30, 2010
Stock Repurchase Right
Sep. 30, 2007
Stock Repurchase Right
Dec. 31, 2012
Restricted Stock
Dec. 31, 2011
Restricted Stock
Dec. 31, 2010
Restricted Stock
Dec. 31, 2012
Restricted Stock
Modification of Exercise Price
Dec. 31, 2012
Restricted Stock
Modification of Exercise Price
After Modification
Dec. 31, 2012
Restricted Stock
Modification of Exercise Price
Before Modification
Dec. 31, 2012
Restricted Stock
Conversion of Options to restricted shares
Dec. 31, 2012
Nonvested Stock Option
Modification of Exercise Price
Dec. 31, 2012
Vested Stock Options
Modification of Exercise Price
Dec. 31, 2012
Stock Incentive Plan 2008
Dec. 31, 2012
Stock Incentive Plan 2010
Dec. 31, 2012
Stock Incentive Plan 2010
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                                          
Maximum number of shares that may be issued as a percentage of outstanding stock                                                     8.00% 10.00%  
Maximum number of shares that may be issued                                                       2,315,000  
Stock incentive plans, term                                 4 years                       10 years
Stock incentive vested on first anniversary                                 25.00%                       25.00%
Stock incentive vesting ratably over the following 36 months                                 75.00%                       75.00%
Weighted average grant date fair value of options granted        $ 12.09 $ 5.62                                                
Options exercised     75,694 66,961                                                   
Option exercise price     $ 9.44 $ 11.78       $ 0 $ 9.52       $ 12.12 $ 6.06 $ 19.81             $ 0 $ 5.58            
Incremental compensation cost related to plan modified                                         $ 200,000     $ 2,200,000 $ 700,000 $ 200,000      
Unrecognized compensation expense related to unvested share options                                                           
Shares subject to transfer restrictions   10,800,000                                                      
Share-based compensation     3,998,548 2,156,710 2,220,167         1,437,201 2,014,692 794,665       919,221   2,561,347 142,018 1,425,502                  
Unrecognized compensation expense, period for recognition                                   2 years     2 years                
Restricted shares granted 11,000   11,000                                   150,000                
Percentage of restricted shares vested immediately 25.00%                                                        
Restricted shares granted, vesting percentage           25.00% 50.00%                                            
Total fair value of non-vested restricted shares     2,144,851 259,219 1,370,250                                                
Unrecognized compensation expense related to non-vested restricted shares     $ 6,849,214