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Financial Instruments and Risk Management - Credit and Liquidity Risk (Details) - USD ($)
Dec. 31, 2017
Feb. 28, 2017
Dec. 31, 2016
Disclosure of continuing involvement in derecognised financial assets [line items]      
Percent of gross accounts receivable over 90 days past due (less than) 1.00%    
Allowance for doubtful accounts $ 4,300,000   $ 3,100,000
Factoring of receivables from facility program      
Disclosure of continuing involvement in derecognised financial assets [line items]      
Agreement to sell trade receivables, maximum capacity $ 200,000,000 $ 250,000,000.0