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Investment in ATC (Details-1) (USD $) | 3 Months Ended | 4 Months Ended |  |  | 3 Months Ended
--- | --- | --- | --- | --- | ---
Mar. 31, 2013 | Mar. 31, 2012 | Apr. 30, 2013 Mge Transco [Member] ATC Capital Contribution [Member] | Mar. 31, 2013 ATC [Member] | Dec. 31, 2012 ATC [Member] | Mar. 31, 2013 ATC [Member] Mge Transco [Member] | Mar. 31, 2012 ATC [Member] Mge Transco [Member]
Equity method investments [Line Items] |  |  |  |  |  |  |
Equity earnings from investment in ATC | $ 2,396,000 | $ 2,242,000 |  |  |  | $ 2,400,000 | $ 2,200,000
Dividend income from ATC | 1,807,000 | 1,740,000 |  |  |  | 1,800,000 | 1,700,000
Contributions to ATC |  |  |  |  |  | 200,000 | 400,000
Investment in ATC |  |  |  | 61,800,000 | 61,000,000 |  |
Subsequent Events [Line Items] |  |  |  |  |  |  |
Subsequent Event, Description |  |  | On April 30, 2013, MGE Transco made a $0.5 million capital contribution to ATC. |  |  |  |
Contributions to ATC | $ 373,000 | $ 355,000 | $ 500,000 |  |  |  |

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