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Debt - Additional Information (Detail) - Multi currency revolving credit agreement [Member] - USD ($)
9 Months Ended
Sep. 30, 2017
Dec. 31, 2016
Debt Instrument [Line Items]    
Revolving credit agreement $ 125,000,000  
Credit agreement expiry Date Jul. 10, 2019  
Letters of Credit Outstanding $ 4,677,000  
Outstanding borrowing 0  
Unused Revolving credit 120,323,000  
Unrestricted retained earnings $ 200,112,000 $ 157,606,000