Income Taxes Schedule of Effective Income Tax Rate Reconciliation (Details)	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Income Taxes [Abstract]
Federal statutory tax rate	35.00%	35.00%	35.00%
Federal tax credits	(12.70%)	(10.40%)	(8.30%)
State and local taxes, net of federal tax benefit	2.60%	4.40%	3.40%
Flow through depreciation and cost basis differences	2.10%	0.10%	(1.60%)
Investment tax credit amortization	0.00%	0.00%	(1.50%)
Other	1.30%	1.20%	1.80%
Effective tax rate	28.30%	30.30%	28.80%

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A ratio calculated by dividing the reported amount of income tax expense attributable to continuing operations for the period by GAAP-basis pretax income from continuing operations.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

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-Section 50

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-Subparagraph (SX 210.4-08.(h)(2))

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-Publisher FASB

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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The domestic federal statutory tax rate applicable under enacted tax laws to the Company's pretax income from continuing operations for the period. The "statutory" tax rate is the regular tax rate if there are alternative tax systems.

+ References

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

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-Name Accounting Standards Codification

-Topic 740

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate that can be explained by the different depreciation methods allowed under generally accepted accounting principles and enacted tax laws.

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

-Publisher FASB

-Name Accounting Standards Codification

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The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate attributable to all other items not otherwise listed in the existing taxonomy.

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The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate that can be explained by the state and local income tax expense or benefit, net of the federal tax benefit (expense) thereon, recorded during the period.

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The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate that can be explained by investment tax credits generated or utilized under enacted tax laws during the period.

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The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate that can be explained by tax credits, not otherwise listed in the existing taxonomy, generated or utilized under enacted tax laws during the period.

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