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Fair Value Accounting, Fair Values of Derivative Instruments (Details) (Derivatives Not Designated As Hedging Instruments [Member], USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Fair values of derivative instruments [Abstract]
Total	$ (3,308)	$ (5,336)
Energy Risk Management Liability, Net [Member] \| Fuel Cost Hedges [Member]
Fair values of derivative instruments [Abstract]
Current	$ (3,308)	$ (5,336)

Fair value of derivative liability, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position.

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