Fair Value Measurements (Narrative) (Details) - Cash flow hedging - Derivatives designated as hedging instruments: - Fixed price diesel swaps gal in Millions	Sep. 30, 2017 $ / gal gal
Derivatives, Fair Value [Line Items]
Fixed price swap contract (in gallons) \| gal	2.7
Average forward price (in dollars per gallon)	2.58
Average forward price of hedged item (in dollars per gallon)	2.78

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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