2.4.0.8020000 - Disclosure - Significant Accounting Policies (Policies)truefalsefalse1false falsefalseFROM_Jan01_2013_TO_Jun30_2013http://www.sec.gov/CIK0001161728duration2013-01-01T00:00:002013-06-30T00:00:001true 1mgee_SignificantAccountingPoliciesAbstractmgee_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00falsefalsefalsexbrli:stringItemTypestringfalse0Significant Accounting Policies [Abstract]2false 2us-gaap_ConsolidationVariableInterestEntityPolicyus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00MGE Power Elm Road and MGE Power West Campus own electric generating assets and lease those assets to MGE. Both entities are variable interest entities under applicable authoritative guidance. MGE is considered the primary beneficiary of these entities as a result of contractual agreements. As a result, MGE has consolidated MGE Power Elm Road and MGE Power West Campus.falsefalsefalsenonnum:textBlockItemTypenaDisclosure of accounting policy for consolidation to describe the significant judgments and assumptions made in determining whether a variable interest held by the entity requires the variable interest entity to be consolidated and (or) disclose information about its involvement with the variable interest entity; the methodology used by the entity for determining whether or not it is the primary beneficiary of the variable interest entity; and the significant factors considered and judgments made in determining that the power to direct the activities that significantly impact the economic performance of the variable interest entity are shared (as defined).Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6367646&loc=d3e18780-107790 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -URI http://asc.fasb.org/subtopic&trid=2197480 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Interpretation (FIN) -Number 46R -Paragraph 14, 15 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 5A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=7880789&loc=SL6759159-111685 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 4 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=7880789&loc=d3e5728-111685 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 2AA -Subparagraph a -URI http://asc.fasb.org/extlink&oid=7880789&loc=SL6759068-111685 Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 167 -Paragraph 24 -Subparagraph e -Appendix D Reference 8: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 167 -Paragraph 22E -Subparagraph a -Appendix D Reference 9: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 167 -Paragraph 22B -Subparagraph a -Appendix D false0Basis of Presentation3false 2us-gaap_ShareBasedCompensationOptionAndIncentivePlansPolicyus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00In addition to units granted in 2009 through 2012, on February 15, 2013, 15,256 units were granted based on the MGE Energy closing stock price as of that date. These units are subject to a five-year graded vesting schedule. On the grant date, MGE Energy and MGE measure the cost of the employee services received in exchange for a performance unit award based on the current market value of MGE Energy common stock. The fair value of the awards has been subsequently re-measured at June 30, 2013, as required by applicable accounting standards. Changes in fair value have been recognized as compensation cost. Since this amount is re-measured quarterly throughout the vesting period, the compensation cost is subject to variability.  For nonretirement eligible employees, stock based compensation costs are accrued and recognized using the graded vesting method. Compensation cost for retirement eligible employees or employees that will become retirement eligible during the vesting schedule are recognized on an abridged horizon. In the event of a bona fide retirement, not followed by work for a competitor, the executive will receive full vesting credit for each outstanding award.falsefalsefalsenonnum:textBlockItemTypenaDisclosure of accounting policy for stock option and stock incentive plans. This disclosure may include (1) the types of stock option or incentive plans sponsored by the entity (2) the groups that participate in (or are covered by) each plan (3) significant plan provisions and (4) how stock compensation is measured, and the methodologies and significant assumptions used to determine that measurement.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6367646&loc=d3e18780-107790 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 123R -Paragraph A240 -Subparagraph a -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b),(f) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -URI http://asc.fasb.org/subtopic&trid=2228939 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Emerging Issues Task Force (EITF) -Number 06-11 -Paragraph 7 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. false0Share-based Compensation4false 2us-gaap_DerivativesMethodsOfAccountingHedgingDerivativesus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00As part of its regular operations, MGE enters into contracts, including options, swaps, futures, forwards, and other contractual commitments, to manage its exposure to commodity prices and gas revenues. To the extent that these contracts are derivatives, MGE assesses whether or not the normal purchases or normal sales exclusion applies. For contracts to which this exclusion cannot be applied, MGE Energy and MGE recognize such derivatives in the consolidated balance sheets at fair value. The majority of MGE's derivative activities are conducted in accordance with its electric and gas risk management program, which is approved by the PSCW and limits the volume MGE can hedge with specific risk management strategies. The maximum length of time over which cash flows related to energy commodities can be hedged is four years. If the derivative qualifies for regulatory deferral, the derivatives are marked to fair value and are offset with a corresponding regulatory asset or liability. The deferred gain or loss is recognized in earnings in the delivery month applicable to the instrument. Gains and losses related to hedges qualifying for regulatory treatment are recoverable in gas rates through the PGA or in electric rates as a component of the fuel rules mechanism.falsefalsefalsenonnum:textBlockItemTypenaDisclosure of accounting policy for derivatives used in hedging relationships, which may include how gains or losses are recognized and presented in the financial statements, and amortization policies for deferred amounts.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624171-113959 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 30 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=7668309&loc=d3e80748-113994 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5618551-113959 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 25 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6886632&loc=d3e76258-113986 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(n)) -URI http://asc.fasb.org/extlink&oid=6881521&loc=d3e23780-122690 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 44 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 08 -Paragraph n -Article 4 false0Derivative Hedging5false 2us-gaap_DerivativesOffsettingFairValueAmountsPolicyus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00All derivative instruments in this table are presented on a gross basis and are calculated prior to the netting of instruments with the same counterparty under a master netting agreement as well as the netting of collateral. For financial statement purposes, MGE Energy and MGE have netted instruments with the same counterparty under a master netting agreement as well as the netting of collateral.falsefalsefalsenonnum:textBlockItemTypenaDisclosure of accounting policy for offsetting or not offsetting fair value amounts recognized for derivative instruments against such amounts recognized for the right to reclaim cash collateral (a receivable) or the obligation to return cash collateral (a payable) arising from derivative instruments recognized at fair value.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=7476318&loc=d3e41675-113959 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Staff Position (FSP) -Number FIN39-1 -Paragraph 10, 10A, 10B -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. false0Derivative Netting6false 2mgee_WisconsinFuelRulesPolicyPolicyTextBlockmgee_falsenadurationfalsefalsefalsefalsefalsefalsefalsefalseterseLabel1falsefalsefalse00Fuel rules require the PSCW and Wisconsin utilities to defer electric fuel-related costs that fall outside a symmetrical cost tolerance band around the amount approved for a utility in its most recent base rate proceedings. Any over/under recovery of the actual costs is determined on an annual basis and will be adjusted in future billings to electric retail customers. The fuel rules bandwidth is currently set at plus or minus 2%. Under fuel rules, MGE would defer costs, less any excess revenues, if its actual electric fuel costs exceeded 102% of the electric fuel costs allowed in its latest rate order. Excess revenues are defined as revenues in the year in question that provide MGE with a greater return on common equity than authorized by the PSCW in MGE's latest rate order. Conversely, MGE is required to defer the benefit of lower costs if actual electric fuel costs were less than 98% of the electric fuel costs allowed in that order.falsefalsefalsenonnum:textBlockItemTypenaDisclosure of accounting policy for any over or under recovery of the electric fuel-related costs that fall outside a symmetrical cost tolerance band.No definition available.false0Wisconsin Fuel Rules7false 2us-gaap_FairValueOfFinancialInstrumentsPolicyus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00Fair value is defined as the price that would be received to sell an asset or would be paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants at the measurement date. The standard clarifies that fair value should be based on the assumptions market participants would use when pricing the asset or liability including assumptions about risk. The standard also establishes a three level fair value hierarchy based upon the observability of the assumptions used and requires the use of observable market data when available. The levels are: Level 1 - Pricing inputs are quoted prices within active markets for identical assets or liabilities. Level 2 - Pricing inputs are quoted prices within active markets for similar assets or liabilities; quoted prices for identical or similar instruments in markets that are not active; and model-derived valuations that are correlated with or otherwise verifiable by observable market data. Level 3 - Pricing inputs are unobservable and reflect management's best estimate of what market participants would use in pricing the asset or liability. Investments include exchange-traded investment securities valued using quoted prices on active exchanges and are therefore classified as Level 1. Derivatives include exchange-traded derivative contracts, over-the-counter transactions, a ten-year purchased power agreement, and FTRs. Most exchange-traded derivative contracts are valued based on unadjusted quoted prices in active markets and are therefore classified as Level 1. A small number of exchange-traded derivative contracts are valued using quoted market pricing in markets with insufficient volumes and are therefore classified as Level 3. Transactions done with an over-the-counter party are on inactive markets and are therefore classified as Level 3. These transactions are valued based on quoted prices from markets with similar exchange traded transactions. FTRs are priced based upon monthly auction results for identical or similar instruments in a closed market with limited data available and are therefore classified as Level 3.  The ten-year purchased power agreement (see Footnote 9) was valued using an internally-developed pricing model and therefore is classified as Level 3. The model projects future market energy prices and compares those prices to the projected power costs to be incurred under the contract. Inputs to the model require significant management judgment and estimation. Future energy prices are based on a forward power pricing curve using exchange-traded contracts in the electric futures market, where such exchange-traded contracts exist, and upon calculations based on forward gas prices, where such exchange-traded contracts do not exist. A basis adjustment is applied to the market energy price to reflect the price differential between the market price delivery point and the counterparty delivery point. The historical relationship between the delivery points is reviewed and a discount (below 100%) or premium (above 100%) is derived. This comparison is done for both peak times when demand is high and off peak times when demand is low. If the basis adjustment is lowered, the fair value measurement will decrease and if the basis adjustment is increased, the fair value measurement will increase. The projected power costs anticipated to be incurred under the purchased power agreement are determined using many factors, including historical generating costs, future prices, and expected fuel mix of the counterparty. An increase in the projected fuel costs would result in a decrease in the fair value measurement of the purchased power agreement. A significant input that MGE estimates is the counterparty's fuel mix in determining the projected power cost. MGE also considers the assumptions that market participants would use in valuing the asset or liability. This consideration includes assumptions about market risk such as liquidity, volatility, and contract duration. The fair value model uses a discount rate that incorporates discounting, credit, and model risks. This model is prepared by members of MGE's Energy Supply group. It is reviewed on a quarterly basis by management in Energy Supply and Finance to review the assumptions, inputs, and fair value measurements. The following table presents the significant unobservable inputs used in the pricing model.<div><table style="border-collapse:collapse;margin-top:20px;"><tr style="height: 15px"><td style="width: 125px; text-align:left;border-color:#000000;min-width:125px;"> </td><td style="width: 265px; border-bottom-style:solid;border-bottom-width:1px;text-align:left;border-color:#000000;min-width:265px;">Significant Unobservable Inputs</td><td style="width: 10px; border-bottom-style:solid;border-bottom-width:1px;text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 101px; border-bottom-style:solid;border-bottom-width:1px;text-align:center;border-color:#000000;min-width:101px;">Model Input</td><td style="width: 125px; text-align:left;border-color:#000000;min-width:125px;"> </td></tr><tr style="height: 15px"><td style="width: 125px; text-align:left;border-color:#000000;min-width:125px;"> </td><td style="width: 265px; border-top-style:solid;border-top-width:1px;text-align:left;border-color:#000000;min-width:265px;">Basis adjustment:</td><td style="width: 10px; border-top-style:solid;border-top-width:1px;text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 101px; border-top-style:solid;border-top-width:1px;text-align:center;border-color:#000000;min-width:101px;"> </td><td style="width: 125px; text-align:left;border-color:#000000;min-width:125px;"> </td></tr><tr style="height: 15px"><td style="width: 125px; text-align:left;border-color:#000000;min-width:125px;"> </td><td style="width: 265px; text-align:left;border-color:#000000;min-width:265px;"> On peak</td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 101px; text-align:center;border-color:#000000;min-width:101px;">96.3%</td><td style="width: 125px; text-align:left;border-color:#000000;min-width:125px;"> </td></tr><tr style="height: 15px"><td style="width: 125px; text-align:left;border-color:#000000;min-width:125px;"> </td><td style="width: 265px; text-align:left;border-color:#000000;min-width:265px;"> Off peak</td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 101px; text-align:center;border-color:#000000;min-width:101px;">95.7%</td><td style="width: 125px; text-align:left;border-color:#000000;min-width:125px;"> </td></tr><tr style="height: 15px"><td style="width: 125px; text-align:left;border-color:#000000;min-width:125px;"> </td><td style="width: 265px; text-align:left;border-color:#000000;min-width:265px;">Counterparty fuel mix:</td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 101px; text-align:center;border-color:#000000;min-width:101px;"> </td><td style="width: 125px; text-align:left;border-color:#000000;min-width:125px;"> </td></tr><tr style="height: 15px"><td style="width: 125px; text-align:left;border-color:#000000;min-width:125px;"> </td><td style="width: 265px; text-align:left;border-color:#000000;min-width:265px;"> Internal generation</td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 101px; text-align:center;border-color:#000000;min-width:101px;">50 % - 70 %</td><td style="width: 125px; text-align:left;border-color:#000000;min-width:125px;"> </td></tr><tr style="height: 15px"><td style="width: 125px; text-align:left;border-color:#000000;min-width:125px;"> </td><td style="width: 265px; text-align:left;border-color:#000000;min-width:265px;"> Purchased power</td><td style="width: 10px; text-align:left;border-color:#000000;min-width:10px;"> </td><td style="width: 101px; text-align:center;border-color:#000000;min-width:101px;">50 % - 30 %</td><td style="width: 125px; text-align:left;border-color:#000000;min-width:125px;"> </td></tr></table></div>The deferred compensation plan allows participants to defer certain cash compensation into a notional investment account. These amounts are included within other deferred liabilities in the consolidated balance sheets of MGE Energy and MGE. The notional investments earn interest based upon the semiannual rate of U.S. Treasury Bills having a 26 week maturity increased by 1% compounded monthly with a minimum annual rate of 7%, compounded monthly. The notional investments are based upon observable market data, however, since the deferred compensation obligations themselves are not exchanged in an active market, they are classified as Level 2.falsefalsefalsenonnum:textBlockItemTypenaDisclosure of accounting policy for determining the fair value of financial instruments.Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6367646&loc=d3e18780-107790 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -URI http://asc.fasb.org/subtopic&trid=2155942 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 107 -Paragraph 8, 10, 12, 13, 14 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. false0Recurring Fair Value Measurements8false 2us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlockus-gaap_truenadurationfalsefalsefalsefalsefalsefalsefalsefalse1falsefalsefalse00a.       Presentation of Comprehensive Income.        In February 2013, the FASB issued authoritative guidance within the Codification's Comprehensive Income topic that provides guidance on the reporting of amounts reclassified out of accumulated other comprehensive income. Reclassification adjustments will be presented either on the financial statement where income is presented or as a separate disclosure in the notes to the financial statements. This authoritative guidance became effective January 1, 2013. The authoritative guidance had no effect on our financial statement presentation or notes to the financial statements. b.       Disclosures about Offsetting Assets and Liabilities.        In December 2011, the FASB issued authoritative guidance within the Codification's Balance Sheet topic that provides guidance on disclosures about offsetting assets and liabilities. The new disclosure requirements mandate that entities disclose both gross and net information for instruments and transactions eligible for offset in the balance sheet as well as instruments and transactions subject to a master netting arrangement. In addition, the standard requires disclosure of collateral received and posted in connections with a master netting arrangement. On January 31, 2013, the FASB issued additional authoritative guidance which clarified the scope of disclosures about offsetting assets and liabilities. The revised guidance limits the scope of the new balance sheet offsetting disclosures to derivatives, repurchase agreements, and securities lending transactions to the extent that they are (1) offset in the financial statements or (2) subject to an enforceable master netting arrangement or similar agreement. This authoritative guidance became effective January 1, 2013. The authoritative guidance did not have a financial impact, but required additional disclosures. See Footnote 9 for additional information. c.       Obligations Resulting from Joint and Several Liability Arrangements for Which the Total Amount of the Obligation Is Fixed at the Reporting Date. In February 2013, the FASB issued authoritative guidance within the Codification's Balance Sheet topic that provides guidance on the recognition, measurement, and disclosure of obligations resulting from joint and several liability arrangements for which the total amount of the obligation is fixed at the reporting date. This authoritative guidance will become effective January 1, 2014. The authoritative guidance will not have a financial or disclosure impact. d.        Presentation of an Unrecognized Tax Benefit. In July 2013, the FASB issued authoritative guidance within the Codification's Income Statement topic that provides guidance on the presentation of an unrecognized tax benefit when a net operating loss carryforward, a similar tax loss, or a tax credit carryforward exist. The authoritative guidance was issued to eliminate diversity in practice by providing guidance on the presentation of unrecognized tax benefits. This authoritative guidance will become effective January 1, 2014. The authoritative guidance will not have a financial statement or disclosure impact, unless MGE Energy or its subsidiaries are in a net operating loss position.falsefalsefalsenonnum:textBlockItemTypenaDisclosure of the adoption of new accounting pronouncements that may impact the entity's financial reporting.No definition available.false0New Accounting PronouncementsfalseSignificant Accounting Policies (Policies)UnKnownUnKnownUnKnownUnKnowntruefalsefalseSheethttp://www.mgeenergy.com/role/DisclosureSignificantAccountingPoliciesPolicies18