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Debt - Additional Information (Detail) - USD ($)
9 Months Ended
Jul. 10, 2015
Sep. 30, 2015
Dec. 31, 2014
Unsecured Private Placement Loan      
Debt Instrument [Line Items]      
Unsecured private placement loan $ 100,000,000    
Debt instrument interest rate percentage 3.95%    
Private placement loan, maturity date range, start Jul. 10, 2021    
Private placement loan, maturity date range, end Jul. 10, 2027    
Multi currency revolving credit agreement [Member]      
Debt Instrument [Line Items]      
Revolving credit agreement   $ 125,000,000  
Credit agreement expiry Date   Jul. 10, 2019  
Letters of Credit Outstanding   $ 4,952,000  
Debt Outstanding   0  
Unused Revolving credit   120,048,000  
Unrestricted retained earnings   $ 118,427,000 $ 88,684,000