Regional Transmission Organizations	12 Months Ended
Dec. 31, 2011
Regional Transmission Organizations Disclosure [Abstract]
Regional Transmission Organizations	15. Regional Transmission Organizations - MGE Energy and MGE. MISO MGE is a nontransmission owning member of the MISO. MISO, a FERC approved RTO, is responsible for monitoring the electric transmission system that delivers power from generating plants to wholesale power transmitters. MISO's role is to ensure equal access to the transmission system and to maintain or improve electric system reliability in the Midwest. MISO maintains a bid-based energy market. MGE offers substantially all of its generation on the MISO market and purchases much of its load requirement from the MISO market in accordance with the MISO Tariff. MGE participates in the ancillary services market (ASM) operated by MISO. The ASM is an extension of the existing energy market in which MISO assumes the responsibility of maintaining sufficient generation reserves. In the ASM, MISO provides the reserves for MGE's load, and MGE may offer to sell reserves from its generating units. MGE participates in the voluntary capacity auction, which provides an optional monthly forum for buyers and sellers of aggregate planning resource credits to interact. Load serving entities may participate in the voluntary capacity auction potentially to obtain the necessary aggregate planning resource credits needed to meet their planning reserve margin requirement. Generator owners may participate to sell any excess aggregate planning resource credits that are not needed by them. PJM MGE is a member of PJM. PJM, an RTO, is a neutral and independent party that coordinates and directs the operation of the transmission grid within its area of coverage, administers a competitive wholesale electricity market, and plans regional transmission expansion improvements to maintain grid reliability and relieve congestion. MGE has one purchase power agreement, for a total of 50 MW, with a generator that is located within this market. MGE reports on a net basis transactions on the MISO and PJM markets in which it buys and sells power within the same hour to meet electric energy delivery requirements. This treatment resulted in a $102.1 million, $94.9 million, and $74.4 million reduction to sales to the market and purchased power expense for the years ended December 31, 2011, 2010, and 2009, respectively.

Regional Transmission Organizations

12 Months Ended

Dec. 31, 2011

Regional Transmission Organizations Disclosure [Abstract]

15. Regional Transmission Organizations - MGE Energy and MGE.

MISO

MGE is a nontransmission owning member of the MISO. MISO, a FERC approved RTO, is responsible for monitoring the electric transmission system that delivers power from generating plants to wholesale power transmitters. MISO's role is to ensure equal access to the transmission system and to maintain or improve electric system reliability in the Midwest.

MISO maintains a bid-based energy market. MGE offers substantially all of its generation on the MISO market and purchases much of its load requirement from the MISO market in accordance with the MISO Tariff. MGE participates in the ancillary services market (ASM) operated by MISO. The ASM is an extension of the existing energy market in which MISO assumes the responsibility of maintaining sufficient generation reserves. In the ASM, MISO provides the reserves for MGE's load, and MGE may offer to sell reserves from its generating units.

MGE participates in the voluntary capacity auction, which provides an optional monthly forum for buyers and sellers of aggregate planning resource credits to interact. Load serving entities may participate in the voluntary capacity auction potentially to obtain the necessary aggregate planning resource credits needed to meet their planning reserve margin requirement. Generator owners may participate to sell any excess aggregate planning resource credits that are not needed by them.

PJM

MGE is a member of PJM. PJM, an RTO, is a neutral and independent party that coordinates and directs the operation of the transmission grid within its area of coverage, administers a competitive wholesale electricity market, and plans regional transmission expansion improvements to maintain grid reliability and relieve congestion. MGE has one purchase power agreement, for a total of 50 MW, with a generator that is located within this market.

MGE reports on a net basis transactions on the MISO and PJM markets in which it buys and sells power within the same hour to meet electric energy delivery requirements. This treatment resulted in a $102.1 million, $94.9 million, and $74.4 million reduction to sales to the market and purchased power expense for the years ended December 31, 2011, 2010, and 2009, respectively.