Adoption of Accounting Principles and Recently Issued Accounting Pronouncements	6 Months Ended
Jun. 30, 2018
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
New Accounting Pronouncements	New Accounting Standards - MGE Energy and MGE. a. Recently Adopted Revenue from Contracts with Customers. The FASB issued authoritative guidance within the codification's Revenue Recognition topic that provides guidance on the recognition, measurement, and disclosure of revenue from contracts with customers. The new standard establishes a five-step model for recognizing and measuring revenue from contracts with customers and replaces existing guidance on revenue recognition. The underlying principle is that an entity will recognize revenue to depict the transfer of goods or services to customers at an amount that the entity expects to be entitled to in exchange for those goods or services. This authoritative guidance became effective January 1, 2018, and MGE Energy and MGE adopted the standard upon the effective date. Adoption of this standard is permitted under one of two methods: the full retrospective method or the modified retrospective method. MGE Energy and MGE implemented the standard using the modified retrospective method. The cumulative impact of this guidance on our financial statements is not material, except for additional footnote disclosures. See Footnote 3 for further information. Financial Instruments. In January 2016, the FASB issued authoritative guidance within the codification's Financial Instruments topic that provides guidance on the recognition and measurement of financial instruments. This authoritative guidance became effective January 1, 2018 and required equity investments to be measured at fair value with changes in fair value recognized in net income rather than in other comprehensive income. As a result of this guidance, MGE Energy and MGE will no longer have other comprehensive income related to equity investments. This standard was applied using a modified retrospective approach, with a cumulative effect adjustment recorded to opening retained earnings as of the beginning of the fiscal year of adoption. As of January 1, 2018, MGE Energy recorded a $0.4 million increase in retained earnings and a corresponding decrease in accumulated other comprehensive income, and MGE recorded less than a $0.1 million decrease in retained earnings and a corresponding increase in accumulated other comprehensive income, related to equity investments within the scope of this standard. Restricted Cash. In November 2016, the FASB issued authoritative guidance within the codification's Statement of Cash Flows topic that provides guidance on the classification and presentation of changes in restricted cash within the statement of cash flows. Under the new guidance, reporting entities are required to explain the changes in the total of restricted and unrestricted cash and cash equivalents when reconciling the beginning and ending balances on the statement of cash flows. Prior to the authoritative guidance, changes in restricted cash were presented as either cash flows from operating, investing, or financing activities within the statement of cash flows, as appropriate based on the nature of the restriction. Also under the new standard, reporting entities are required to provide a reconciliation from the balance sheet to the statement of cash flows and disclose the nature of the restrictions of cash. This authoritative guidance became effective January 1, 2018. Upon the effective date, MGE Energy and MGE changed the presentation of restricted cash on the consolidated statements of cash flows to reflect the new accounting guidance retrospectively to all periods presented. See Footnote 1.b. for further information. Pension and Other Postretirement Benefits. In March 2017, the FASB issued authoritative guidance within the codification's Compensation – Retirement Benefits topic that provides guidance on the presentation of net periodic pension cost and net periodic postretirement benefit cost (together, net benefit cost). This authoritative guidance became effective January 1, 2018. Under the new guidance, the service cost component of net benefit cost is required to be recorded in the same line item or items as other compensation costs arising from services rendered by the pertinent employees during the period. The other components of net benefit cost are required to be presented in the income statement separately from the service cost component and outside of income from operations. A practical expedient within the standard permits an employer to use the amounts disclosed in its pension and other postretirement benefit plan footnote for prior comparative periods as the estimation basis for applying the retrospective presentation requirements. MGE Energy and MGE have elected to apply the practical expedient. Upon the effective date, MGE Energy and MGE changed the presentation of net benefit cost on the consolidated statements of income to reflect the new accounting guidance retrospectively to all periods presented. For both MGE Energy and MGE, "Other operations and maintenance expense" increased and "Other income, net" increased $0.9 million and $2.0 million for the three and six months ended June 30, 2017, respectively. The standard also only allows the service cost component to be eligible for capitalization prospectively from the effective date of the pronouncement (whereas under previous GAAP, all components of net benefit cost were eligible for capitalization). See Footnote 6 for further information. b. Recently Issued Leases. In February 2016, the FASB issued authoritative guidance within the codification's Leases topic that provides guidance on the classification, recognition, measurement, and disclosure of leases. The new leasing standard establishes that a lease conveys the right to control the use of identified property, plant, or equipment for a period of time in exchange for consideration. Under the new guidance, lessees will be required to recognize all leases with terms greater than one year, including operating leases, on the balance sheet by recording a right-of-use asset and lease liability. Prior to the authoritative guidance, only capital leases were recognized on the balance sheet by lessees. The new accounting guidance, as applied by lessors, is materially consistent with current GAAP. In January 2018, the FASB issued authoritative guidance which provided an optional practical expedient to grandfather the accounting for existing and expired land easements not accounted for as a lease under the new authoritative guidance. MGE Energy and MGE plan to adopt this practical expedient. Management has begun utilizing a bottoms-up approach to analyze the impact of the standard on our lease portfolio. MGE Energy and MGE have been reviewing current accounting policies and procedures to identify potential differences in accounting treatment that would result from applying the requirements of the new standard to our existing lease portfolio. In addition, we are identifying appropriate changes to our business processes, systems, and controls to support recognition and disclosure requirements under the new standard. This authoritative guidance will become effective January 1, 2019, with early adoption permitted. MGE Energy and MGE anticipate adopting the standard upon the effective date. The new leasing standard requires entities to recognize and measure leases at the beginning of the earliest comparative period presented using a modified retrospective approach. MGE Energy and MGE are currently assessing the impact this pronouncement will have on our financial statements.

New Accounting Standards - MGE Energy and MGE.

a. Recently Adopted

Revenue from Contracts with Customers.

The FASB issued authoritative guidance within the codification's Revenue Recognition topic that provides guidance on the recognition, measurement, and disclosure of revenue from contracts with customers. The new standard establishes a five-step model for recognizing and measuring revenue from contracts with customers and replaces existing guidance on revenue recognition. The underlying principle is that an entity will recognize revenue to depict the transfer of goods or services to customers at an amount that the entity expects to be entitled to in exchange for those goods or services.

This authoritative guidance became effective January 1, 2018, and MGE Energy and MGE adopted the standard upon the effective date. Adoption of this standard is permitted under one of two methods: the full retrospective method or the modified retrospective method. MGE Energy and MGE implemented the standard using the modified retrospective method. The cumulative impact of this guidance on our financial statements is not material, except for additional footnote disclosures. See Footnote 3 for further information.

Financial Instruments.

In January 2016, the FASB issued authoritative guidance within the codification's Financial Instruments topic that provides guidance on the recognition and measurement of financial instruments. This authoritative guidance became effective January 1, 2018 and required equity investments to be measured at fair value with changes in fair value recognized in net income rather than in other comprehensive income. As a result of this guidance, MGE Energy and MGE will no longer have other comprehensive income related to equity investments. This standard was applied using a modified retrospective approach, with a cumulative effect adjustment recorded to opening retained earnings as of the beginning of the fiscal year of adoption. As of January 1, 2018, MGE Energy recorded a $0.4 million increase in retained earnings and a corresponding decrease in accumulated other comprehensive income, and MGE recorded less than a $0.1 million decrease in retained earnings and a corresponding increase in accumulated other comprehensive income, related to equity investments within the scope of this standard.

Restricted Cash.

In November 2016, the FASB issued authoritative guidance within the codification's Statement of Cash Flows topic that provides guidance on the classification and presentation of changes in restricted cash within the statement of cash flows. Under the new guidance, reporting entities are required to explain the changes in the total of restricted and unrestricted cash and cash equivalents when reconciling the beginning and ending balances on the statement of cash flows. Prior to the authoritative guidance, changes in restricted cash were presented as either cash flows from operating, investing, or financing activities within the statement of cash flows, as appropriate based on the nature of the restriction. Also under the new standard, reporting entities are required to provide a reconciliation from the balance sheet to the statement of cash flows and disclose the nature of the restrictions of cash. This authoritative guidance became effective January 1, 2018. Upon the effective date, MGE Energy and MGE changed the presentation of restricted cash on the consolidated statements of cash flows to reflect the new accounting guidance retrospectively to all periods presented. See Footnote 1.b. for further information.

Pension and Other Postretirement Benefits.

In March 2017, the FASB issued authoritative guidance within the codification's Compensation – Retirement Benefits topic that provides guidance on the presentation of net periodic pension cost and net periodic postretirement benefit cost (together, net benefit cost). This authoritative guidance became effective January 1, 2018. Under the new guidance, the service cost component of net benefit cost is required to be recorded in the same line item or items as other compensation costs arising from services rendered by the pertinent employees during the period. The other components of net benefit cost are required to be presented in the income statement separately from the service cost component and outside of income from operations. A practical expedient within the standard permits an employer to use the amounts disclosed in its pension and other postretirement benefit plan footnote for prior comparative periods as the estimation basis for applying the retrospective presentation requirements. MGE Energy and MGE have elected to apply the practical expedient. Upon the effective date, MGE Energy and MGE changed the presentation of net benefit cost on the consolidated statements of income to reflect the new accounting guidance retrospectively to all periods presented. For both MGE Energy and MGE, "Other operations and maintenance expense" increased and "Other income, net" increased $0.9 million and $2.0 million for the three and six months ended June 30, 2017, respectively. The standard also only allows the service cost component to be eligible for capitalization prospectively from the effective date of the pronouncement (whereas under previous GAAP, all components of net benefit cost were eligible for capitalization). See Footnote 6 for further information.

b. Recently Issued

Leases.

In February 2016, the FASB issued authoritative guidance within the codification's Leases topic that provides guidance on the classification, recognition, measurement, and disclosure of leases. The new leasing standard establishes that a lease conveys the right to control the use of identified property, plant, or equipment for a period of time in exchange for consideration. Under the new guidance, lessees will be required to recognize all leases with terms greater than one year, including operating leases, on the balance sheet by recording a right-of-use asset and lease liability. Prior to the authoritative guidance, only capital leases were recognized on the balance sheet by lessees. The new accounting guidance, as applied by lessors, is materially consistent with current GAAP. In January 2018, the FASB issued authoritative guidance which provided an optional practical expedient to grandfather the accounting for existing and expired land easements not accounted for as a lease under the new authoritative guidance. MGE Energy and MGE plan to adopt this practical expedient.

Management has begun utilizing a bottoms-up approach to analyze the impact of the standard on our lease portfolio. MGE Energy and MGE have been reviewing current accounting policies and procedures to identify potential differences in accounting treatment that would result from applying the requirements of the new standard to our existing lease portfolio. In addition, we are identifying appropriate changes to our business processes, systems, and controls to support recognition and disclosure requirements under the new standard. This authoritative guidance will become effective January 1, 2019, with early adoption permitted. MGE Energy and MGE anticipate adopting the standard upon the effective date. The new leasing standard requires entities to recognize and measure leases at the beginning of the earliest comparative period presented using a modified retrospective approach. MGE Energy and MGE are currently assessing the impact this pronouncement will have on our financial statements.