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Derivative Commodity Instruments (Narrative) (Details) (Commodity Forward Contracts [Member], Designated As Fair Value Hedges [Member])	Dec. 31, 2011
Commodity Forward Contracts [Member] | Designated As Fair Value Hedges [Member]
Derivative [Line Items]
Number of derivative instruments, in gallons	57,960,000

X

- Definition

Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 12

+ Details

Name:	invest_DerivativeNonmonetaryNotionalAmount
Namespace Prefix:	invest_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

X

- Details

Name:	us-gaap_DerivativeLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration