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Fair Value of Financial Instruments (Details-1) (USD $) In Thousands, unless otherwise specified | 3 Months Ended |  |  |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Mar. 31, 2013 | Mar. 31, 2013 Maximum [Member] | Mar. 31, 2013 Minimum [Member] | Mar. 31, 2013 Carrying Amount [Member] | Dec. 31, 2012 Carrying Amount [Member] | Mar. 31, 2013 Fair Value [Member] | Dec. 31, 2012 Fair Value [Member] | Mar. 31, 2013 MGE [Member] Carrying Amount [Member] | Dec. 31, 2012 MGE [Member] Carrying Amount [Member] | Mar. 31, 2013 MGE [Member] Fair Value [Member] | Dec. 31, 2012 MGE [Member] Fair Value [Member]
Assets: |  |  |  |  |  |  |  |  |  |  |
Cash and cash equivalents |  |  |  | $ 45,894 | $ 46,357 | $ 45,894 | $ 46,357 | $ 9,856 | $ 6,350 | $ 9,856 | $ 6,350
Liabilities: |  |  |  |  |  |  |  |  |  |  |
Short-term debt - commercial paper |  |  |  | 10,500 | 0 | 10,500 | 0 | 10,500 | 0 | 10,500 | 0
Long-term debt |  |  |  | $ 361,138 | $ 361,805 | $ 432,430 | $ 427,456 | $ 361,138 | $ 361,805 | $ 432,430 | $ 427,456
Significant unobservable inputs [Line Items] |  |  |  |  |  |  |  |  |  |  |
Basis adjustment - on peak | 97.10% |  |  |  |  |  |  |  |  |  |
Basis adjustment - off peak | 96.00% |  |  |  |  |  |  |  |  |  |
Counterparty fuel mix [Abstract] |  |  |  |  |  |  |  |  |  |  |
Internal generation |  | 70.00% | 50.00% |  |  |  |  |  |  |  |
Purchased power |  | 50.00% | 30.00% |  |  |  |  |  |  |  |

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- Definition Estimate of counterparty's internal generation as a portion of their fuel mix, used as an input to measure fair value. + References No definition available. + Details
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- Definition Estimate of counterparty's purchased power as a portion of their fuel mix, used as an input to measure fair value. + References No definition available. + Details
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- Definition Basis adjustment between delivery points for off peak electric future prices. Used as an input to measure fair value. + References No definition available. + Details
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- Definition Basis adjustment between delivery points for on peak electric future prices. Used as an input to measure fair value. + References No definition available. + Details
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- Definition This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents long-term debt obligations meeting the definition of a liability which should be reported as of the balance sheet date. + References No definition available. + Details
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- Definition This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents short-term debt commercial paper obligations meeting the definition of a liability which should be reported as of the balance sheet date. + References No definition available. + Details
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- Definition This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Company may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Cash -URI http://asc.fasb.org/extlink&oid=6506951 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Cash Equivalents -URI http://asc.fasb.org/extlink&oid=6507016 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7, 8, 9, 10 -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 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 7 -Footnote 1 -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 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 8 -Footnote 2 -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. + Details
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