Derivative Commodity Instruments (Narrative) (Details) (Commodity Forward Contracts [Member], Designated As Fair Value Hedges [Member])	Dec. 31, 2012
Commodity Forward Contracts [Member] \| Designated As Fair Value Hedges [Member]
Derivative [Line Items]
Number of derivative instruments, in gallons	46,620,000

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

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 12

-Section 13

-Sentence Column B

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