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Pension and Other Postretirement Plans | 6 Months Ended
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Jun. 30, 2016
Compensation and Retirement Disclosure [Abstract] |
Pension and Other Postretirement Plans | Pension and Other Postretirement Plans - MGE Energy and MGE. MGE maintains qualified and nonqualified pension plans, health care, and life insurance benefits. Additionally, MGE has def ined contribution 401(k) benefit plans. MGE refined its methodology for using discount rates to measure the components of net periodic benefit cost for 2016. The refined methodology uses individual spot rates, instead of a weighted average of the yield curve spot rates, for measuring the servic e cost and interest cost components. The following table presents the components of MGE Energy's and MGE's net periodic benefit costs recognized for the three and six months ended June 30, 2016 and 2015. A portion of the net periodic benefit cost is capitaliz ed within the consolidated balance sheets.
|  |  | Three Months Ended |  | Six Months Ended |
|  |  | June 30, |  | June 30, |
| (In thousands) |  | 2016 |  | 2015 |  | 2016 |  | 2015 |
| Pension Benefits |  |  |  |  |  |  |  |  |
| Components of net periodic cost: |  |  |  |  |  |  |  |  |
| Service cost | $ | 1,564 | $ | 2,039 | $ | 2,945 | $ | 3,837 |
| Interest cost |  | 3,494 |  | 3,902 |  | 6,583 |  | 7,342 |
| Expected return on assets |  | (6,329) |  | (6,438) |  | (11,922) |  | (12,115) |
| Amortization of: |  |  |  |  |  |  |  |  |
| Prior service cost |  | 3 |  | 6 |  | 5 |  | 12 |
| Actuarial loss |  | 1,534 |  | 1,513 |  | 2,890 |  | 2,847 |
| Net periodic cost | $ | 266 | $ | 1,022 | $ | 501 | $ | 1,923 |
| Postretirement Benefits |  |  |  |  |  |  |  |  |
| Components of net periodic (benefit) cost: |  |  |  |  |  |  |  |  |
| Service cost | $ | 399 | $ | 3 | $ | 723 | $ | 386 |
| Interest cost |  | 831 |  | 6 |  | 1,505 |  | 784 |
| Expected return on assets |  | (868) |  | (5) |  | (1,573) |  | (708) |
| Amortization of: |  |  |  |  |  |  |  |  |
| Transition obligation |  | 1 |  | - |  | 2 |  | 1 |
| Prior service benefit |  | (822) |  | (5) |  | (1,489) |  | (672) |
| Actuarial loss |  | 196 |  | 2 |  | 355 |  | 264 |
| Net periodic (benefit) cost | $ | (263) | $ | 1 | $ | (477) | $ | 55 |

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- Definition The entire disclosure for pension and other postretirement benefits. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=49170332&loc=SL14450702-114947 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e2410-114920 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 60 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6414203&loc=d3e39675-114964 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 60 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6414199&loc=d3e39622-114963 + Details
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