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Columbia Environmental Project Construction (Details) (USD $) | 12 Months Ended |  | 12 Months Ended |
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Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2013 Columbia Environmental Project [Member] PSCW [Member] | Dec. 31, 2012 Columbia Environmental Project [Member] PSCW [Member] | Dec. 31, 2011 Columbia Environmental Project [Member] PSCW [Member] | Dec. 31, 2014 Columbia Environmental Project [Member] PSCW [Member] Approved Future Rate Matters [Member] | Dec. 31, 2013 Columbia Units [Member] WPL [Member] | Dec. 31, 2013 Columbia Units [Member] WPSC [Member] | Dec. 31, 2013 MGE [Member] | Dec. 31, 2012 MGE [Member] | Dec. 31, 2011 MGE [Member] | Dec. 31, 2013 MGE [Member] Columbia Environmental Project [Member] | Dec. 31, 2012 MGE [Member] Columbia Environmental Project [Member] | Dec. 31, 2013 MGE [Member] Columbia Units [Member]
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Jointly owned utility plant, ownership interest |  |  |  |  |  |  |  | 46.20% | 31.80% |  |  |  |  |  | 22.00%
Jointly owned utility plant, total expected capital expenditures |  |  |  |  |  |  |  |  |  |  |  |  | $ 135,000,000 |  |
Total incurred costs to date | 141,415,000 | 98,411,000 |  |  |  |  |  |  |  | 141,415,000 | 98,411,000 |  | 120,900,000 |  |
Expected capital expenditures in next fiscal year |  |  |  |  |  |  |  |  |  |  |  |  | 14,000,000 |  |
AFUDC equity recognized |  |  |  |  |  |  |  |  |  | $ 3,140,000 | $ 1,731,000 | $ 413,000 | $ 2,700,000 | $ 1,400,000 |
Authorized AFUDC rate | 50.00% | 50.00% | 50.00% | 50.00% | 100.00% | 100.00% | 100.00% |  |  |  |  |  |  |  |
Authorized rate of return |  |  |  | 50.00% |  |  |  |  |  |  |  |  |  |  |

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- Definition Expected capital expenditures to be incurred during construction of an asset maturing in the next fiscal year following the latest fiscal year. + References No definition available. + Details
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- Definition Total expected capital expenditures to be incurred during construction of an asset. + References No definition available. + Details
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- Definition Rate the company is entitled to earn a return on construction work in progress as approved in the current rate case for the year. + References No definition available. + Details
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- Definition Gross amount, at the balance sheet date, of long-lived assets under construction that include construction costs to date on capital projects that have not been completed and assets being constructed that are not ready to be placed into service. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 12 -Paragraph 5 -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 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229 + Details
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- Definition The proportionate share of interest (percent) in a jointly owned utility plant. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 360 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 10.C) -URI http://asc.fasb.org/extlink&oid=6500719&loc=d3e659983-123033 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 10 -Section C + Details
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- Definition The component of the allowance for funds used during construction during the period based on an assumed rate of return on equity funds used in financing the construction of regulated assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 835 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6501569&loc=d3e55921-110430 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 71 -Paragraph 15 -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 -Name Accounting Standards Codification -Topic 980 -SubTopic 835 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6501662&loc=d3e56162-110433 + Details
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- Definition Disclosure of the effective rate for the period representing (a) total additions to qualifying regulated assets for allowance for funds used during construction, (b) divided by the sum of debt and equity funds used for construction. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 835 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6501569&loc=d3e55921-110430 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 835 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6501662&loc=d3e56162-110433 + Details
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