Derivatives (Narrative) (Details) gal in Millions, CAD in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2016 CAD	Sep. 30, 2016 CAD gal
Diesel swap
Derivative [Line Items]
Fixed price swap contract (in gallons) \| gal		9.8
Foreign contracts
Derivative [Line Items]
Derivative purchases of underlying currency (in Canadian Dollars) \| CAD	CAD 301	CAD 552

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