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Investment in ATC (Details-1) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2016 | Jun. 30, 2015 | Jun. 30, 2016 | Jun. 30, 2015 | Dec. 31, 2015
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |
Equity earnings from investment | $ 1,767 | $ 2,289 | $ 4,000 | $ 4,170 |
Dividend income from investment | 1,863 | 1,471 | 2,728 | 2,891 |
Contributions to investments | 177 | 177 | 998 | 538 |
ATC [Member] |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |
Related party expenses | 7,400 | 7,000 | 14,700 | 14,100 |
Due from related parties | 200 |  | 200 |  | $ 200
MGE Transco [Member] | ATC [Member] |  |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |
Equity earnings from investment | 1,767 | 2,289 | 4,000 | 4,170 |
Dividend income from investment | 1,863 | 1,471 | 2,728 | 2,891 |
Contributions to investments | 177 | 177 | 710 | 355 |
Equity method investment | 71,400 |  | 71,400 |  | 69,500
MGE [Member] |  |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |  |
Equity earnings from investment | 1,767 | 2,289 | 4,000 | 4,170 |
Dividend income from investment | 1,863 | 1,471 | 2,728 | 2,891 |
Contributions to investments | $ 177 | $ 177 | $ 710 | $ 355 |
Minority Interest [Line Items] |  |  |  |  |
MGE's ownership interest in MGE Transco | 51.00% |  | 51.00% |  |
Noncontrolling interest on balance sheet | $ 142,670 |  | $ 142,670 |  | $ 140,308
MGE [Member] | MGE Transco [Member] |  |  |  |  |
Minority Interest [Line Items] |  |  |  |  |
Noncontrolling interest on balance sheet | $ 24,900 |  | $ 24,900 |  |
MGE Energy [Member] |  |  |  |  |
Minority Interest [Line Items] |  |  |  |  |
MGE Energy's ownership interest in MGE Transco | 49.00% |  | 49.00% |  |

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