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Investments (Details-2) - USD ($) $ in Thousands |  | 12 Months Ended
--- | --- | ---
Jan. 29, 2016 | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Schedule Of Equity Method Investments [Line Items] |  |  |  |
Equity in earnings in ATC |  | $ 7,728 | $ 9,150 | $ 9,434
Dividend income from ATC |  | 6,645 | 7,740 | 7,404
Contributions to investments |  | 1,053 | 2,185 | 1,660
MGE Transco [Member] | ATC [Member] |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |
Equity in earnings in ATC |  | 7,728 | 9,150 | 9,434
Dividend income from ATC |  | 6,645 | 7,740 | 7,404
Contributions to investments |  | $ 710 | $ 1,775 | $ 1,420
MGE Transco ownership interest in ATC |  | 3.60% | 3.60% |
MGE Transco [Member] | ATC [Member] | Subsequent Event [Member] |  |  |  |
Schedule Of Equity Method Investments [Line Items] |  |  |  |
Contributions to investments | $ 500 |  |  |

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