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Share repurchase plan - Additional Information (Detail) - USD ($)
1 Months Ended 3 Months Ended
Apr. 25, 2016
Mar. 31, 2016
Dec. 31, 2015
Equity Class Of Treasury Stock [Line Items]      
Share repurchase program, authorized amount     $ 75,000,000
Common stock repurchased, shares   676,259  
Common stock repurchased, amount   $ 26,500,000  
Common stock repurchased, price per share   $ 39.13  
Share repurchase program, remaining authorized amount   $ 37,000,000  
Subsequent Event      
Equity Class Of Treasury Stock [Line Items]      
Common stock repurchased, shares 136,816    
Common stock repurchased, amount $ 5,800,000