v3.8.0.1
Subsequent event - Additional Information (Detail) - USD ($)
$ in Millions
Feb. 28, 2018
Aug. 31, 2017
Subsequent Event [Line Items]    
Amount of repurchased ordinary shares   $ 30.0
Subsequent Event    
Subsequent Event [Line Items]    
Additional amount of repurchased ordinary shares $ 30.0  
Amount of repurchased ordinary shares $ 60.0