Derivatives (Narrative) (Details) (Diesel swap, Fixed price swap contracts)	3 Months Ended
Mar. 31, 2015 gal
Diesel swap \| Fixed price swap contracts
Derivative [Line Items]
Fixed price swap contract (in gallons)	10,600,000

Nominal volume used to calculate payments on a derivative instrument.

No definition available.

Name:	us-gaap_DerivativeNonmonetaryNotionalAmountVolume
Namespace Prefix:	us-gaap_
Data Type:	num:volumeItemType
Balance Type:	na
Period Type:	duration