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Share-based Compensation - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based compensation expenses $ 2.0 $ 1.8 $ 4.2 $ 3.4
Restricted Stock Units        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Maximum unrecognized cost for stock options $ 16.8   $ 16.8  
Unrecognized compensation cost, weighted average period of recognition     2 years 18 days  
Time Based Awards        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period     3 years  
Awards with Performance Conditions | 2015 LTIP        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period     3 years  
Awards with Performance Conditions | 2016 LTIP        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Performance measurement period     1 year  
Requisite service period     2 years  
Awards with Performance Conditions | 2017 LTIP        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period     3 years  
Performance measurement period     1 year  
Requisite service period     2 years  
Performance adjustment percent     25.00%