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Pension Plans and Other Postretirement Benefits (Details-2) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Defined Benefit Plan Deferred Net Periodic Benefit Cost [Abstract] |  |  |  |
Deferred pension and OPRB costs | $ 6,200,000 |  |  |
Pension Benefits [Member] |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |
Service cost | 4,692,000 | [1] | $ 5,723,000 | $ 5,383,000
Interest cost | 14,302,000 | [1] | 12,859,000 | 12,625,000
Expected return on assets | (22,786,000) | [1] | (26,241,000) | (22,963,000)
Amortization of: |  |  |  |
Transition obligation | 0 | [1] | 0 | 0
Prior service (credit) cost | (117,000) | [1] | (44,000) | (17,000)
Actuarial loss | 7,379,000 | [1] | 5,278,000 | 6,352,000
Net periodic benefit cost (credit) | 3,470,000 | [1] | (2,425,000) | 1,380,000
Postretirement Benefits [Member] |  |  |  |
Components of Net Periodic Benefit Cost |  |  |  |
Service cost | 1,110,000 | [1] | 1,283,000 | 1,231,000
Interest cost | 2,893,000 | [1] | 2,612,000 | 2,666,000
Expected return on assets | (2,723,000) | [1] | (3,232,000) | (2,887,000)
Amortization of: |  |  |  |
Transition obligation | 3,000 | [1] | 3,000 | 3,000
Prior service (credit) cost | (2,669,000) | [1] | (2,669,000) | (2,669,000)
Actuarial loss | 401,000 | [1] | 488,000 | 660,000
Net periodic benefit cost (credit) | $ (985,000) | [1] | $ (1,515,000) | $ (996,000)
[1] | MGE has deferred approximately $6.2 million of pension and other postretirement costs. The impact of the deferral has not been reflected in the table above. See Footnote 8 for further information.

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