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Comtemplated Strategic Partner, Ownership Percentage, Maximum

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Estimated Environmental Remediation Costs

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Incremental Operating And Maintenance Costs Approved for Deferral

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Percentage of revenues related to the facility being subject to FERC's jurisdiction.

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

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 13

-Section A

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

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-Name Accounting Standards Codification

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-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 15

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-Name Accounting Standards Codification

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Regulatory Matters (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended	3 Months Ended	9 Months Ended	12 Months Ended			9 Months Ended
	Sep. 30, 2011 South Dakota Rate Case [Member]	Sep. 30, 2011 Wind Generation [Member] watts	Sep. 30, 2011 Montana Distribution System Infrastructure Project [Member]	Dec. 31, 2012 Montana Distribution System Infrastructure Project [Member]	Dec. 31, 2011 Montana Distribution System Infrastructure Project [Member]	Sep. 30, 2011 Montana Distribution System Infrastructure Project [Member] Deferred Project Costs [Member]	Sep. 30, 2011 Dave Gates Generating Station [Member]	Sep. 30, 2011 Mountain States Transmission [Member]
Request Natural Gas Distribution Revenue Increase	$ 4.1
Rate Of Return On Equity For Base Rate	10.90%
Capitalized Structure Percentage Of Equity	56.00%
Rate Base, Natural Gas Distribution	67.5
Estimated Environmental Remediation Costs	1.4
Megawatts of Capacity		40
Estimated Construction Costs		86					202
Deferred Incremental Operating And Maintenence Costs Maximum Amount			16.9
Estimated Incremental Project Costs				9.7	7.2
Deferred costs						2.3
Projected Capital Expenditures			287
Payments for Capital Improvements			8.5
Total Project Costs Incurred to Date							183
Percentage Of Revenue Based On MPSC							80.00%
Percentage Of Revenues Based On FERC							20.00%
Deferred Revenue							8.2
Comtemplated Strategic Partner, Ownership Percentage, Maximum								50.00%
Capitalized Costs Relating to Preliminary Survey And Investigation								$ 19.5