Regulatory matters and revenues subject to refund	9 Months Ended
Sep. 30, 2014
Regulated Operations [Abstract]
Regulatory matters and revenues subject to refund	Regulatory matters and revenues subject to refund On April 8, 2014, Montana-Dakota submitted a request to the NDPSC to update the environmental cost recovery rider to reflect actual costs incurred through February 2014 and projected costs through June 2015 related to the recovery of Montana-Dakota's share of the costs resulting from the environmental retrofit required to be installed at the Big Stone Station. The NDPSC approved the proposed rider on July 10, 2014, reflecting an annual amount of $8.6 million to be recovered under the rider. The rider was effective with service rendered on and after July 15, 2014. On February 27, 2014, Montana-Dakota filed an application with the NDPSC for approval of an electric generation resource recovery rider for recovery of Montana-Dakota's investment in the recently constructed 88-MW simple-cycle natural gas turbine and associated facilities near Mandan, ND. Montana-Dakota requested recovery of $7.4 million annually or approximately 4.6 percent above current rates. Advance determination of prudence and a certificate of public convenience and necessity were received from the NDPSC on April 11, 2012. On March 12, 2014, the NDPSC suspended the filing pending further review. The NDPSC held a hearing regarding this matter on May 28, 2014. On August 20, 2014, the NDPSC approved a settlement agreement reached with the NDPSC staff on May 20, 2014, as amended July 25, 2014, which provides for establishing a generation resource recovery rider and a provision to recover costs associated with a pipeline to the facility through the fuel and purchased power adjustment mechanism. As part of the settlement, the requested recovery for the 88-MW simple-cycle natural gas turbine was established with Montana-Dakota withdrawing the initial rate adjustment and allowing Montana-Dakota the right to file and implement an adjustment within 30 days of filing upon a reasonable showing that the expected return is below a specified return on equity. The settlement also provides for sharing of earnings received by Montana-Dakota in 2014 over a specified return on equity. On August 11, 2014, Montana-Dakota filed an application with the MTPSC for a natural gas rate increase. Montana-Dakota requested a total increase of approximately $3.0 million annually or approximately 3.6 percent above current rates. The requested increase includes the costs associated with the increased investment in facilities, including ongoing investment in new and replacement distribution facilities, depreciation and taxes associated with the increased investment as well as an increase in Montana-Dakota's operation and maintenance expenses. Montana-Dakota requested an interim increase, subject to refund, of $2.2 million or approximately 2.6 percent, which is pending before the MTPSC. On October 3, 2014, Montana-Dakota filed an application with the WYPSC for a natural gas rate increase. Montana-Dakota requested a total increase of approximately $788,000 annually or approximately 4.1 percent above current rates. The requested increase includes the costs associated with the increased investment in facilities, including ongoing investment in new and replacement distribution facilities and the associated operation and maintenance expenses, depreciation and taxes associated with the increase in investment. On October 31, 2013, WBI Energy Transmission filed a general natural gas rate change application with the FERC based on an increase in investments of $312 million, increased operating costs, and the effect of lower storage and off system volumes. On April 30, 2014, WBI Energy Transmission reached a settlement in principle with FERC Trial Staff and all active parties to resolve the rate case. WBI Energy Transmission filed settlement rates to take effect on an interim basis, effective May 1, 2014, pending final approval of the settlement. On June 4, 2014, WBI Energy Transmission submitted to the FERC an Uncontested Offer of Settlement. On June 11, 2014, the Presiding Administrative Law Judge issued a Certification of Uncontested Settlement recommending FERC approval of the settlement without modification. On August 11, 2014, the FERC issued an order approving the settlement without modification and the resulting rates were approved to be effective May 1, 2014. No parties to the proceeding requested rehearing of the order, which is now final. Based on the adjusted base period volumes filed in the case, the annual increase in revenues is approximately $11.5 million.

Regulatory matters and revenues subject to refund

On April 8, 2014, Montana-Dakota submitted a request to the NDPSC to update the environmental cost recovery rider to reflect actual costs incurred through February 2014 and projected costs through June 2015 related to the recovery of Montana-Dakota's share of the costs resulting from the environmental retrofit required to be installed at the Big Stone Station. The NDPSC approved the proposed rider on July 10, 2014, reflecting an annual amount of $8.6 million to be recovered under the rider. The rider was effective with service rendered on and after July 15, 2014.

On February 27, 2014, Montana-Dakota filed an application with the NDPSC for approval of an electric generation resource recovery rider for recovery of Montana-Dakota's investment in the recently constructed 88-MW simple-cycle natural gas turbine and associated facilities near Mandan, ND. Montana-Dakota requested recovery of $7.4 million annually or approximately 4.6 percent above current rates. Advance determination of prudence and a certificate of public convenience and necessity were received from the NDPSC on April 11, 2012. On March 12, 2014, the NDPSC suspended the filing pending further review. The NDPSC held a hearing regarding this matter on May 28, 2014. On August 20, 2014, the NDPSC approved a settlement agreement reached with the NDPSC staff on May 20, 2014, as amended July 25, 2014, which provides for establishing a generation resource recovery rider and a provision to recover costs associated with a pipeline to the facility through the fuel and purchased power adjustment mechanism. As part of the settlement, the requested recovery for the 88-MW simple-cycle natural gas turbine was established with Montana-Dakota withdrawing the initial rate adjustment and allowing Montana-Dakota the right to file and implement an adjustment within 30 days of filing upon a reasonable showing that the expected return is below a specified return on equity. The settlement also provides for sharing of earnings received by Montana-Dakota in 2014 over a specified return on equity.

On August 11, 2014, Montana-Dakota filed an application with the MTPSC for a natural gas rate increase. Montana-Dakota requested a total increase of approximately $3.0 million annually or approximately 3.6 percent above current rates. The requested increase includes the costs associated with the increased investment in facilities, including ongoing investment in new and replacement distribution facilities, depreciation and taxes associated with the increased investment as well as an increase in Montana-Dakota's operation and maintenance expenses. Montana-Dakota requested an interim increase, subject to refund, of $2.2 million or approximately 2.6 percent, which is pending before the MTPSC.

On October 3, 2014, Montana-Dakota filed an application with the WYPSC for a natural gas rate increase. Montana-Dakota requested a total increase of approximately $788,000 annually or approximately 4.1 percent above current rates. The requested increase includes the costs associated with the increased investment in facilities, including ongoing investment in new and replacement distribution facilities and the associated operation and maintenance expenses, depreciation and taxes associated with the increase in investment.

On October 31, 2013, WBI Energy Transmission filed a general natural gas rate change application with the FERC based on an increase in investments of $312 million, increased operating costs, and the effect of lower storage and off system volumes. On April 30, 2014, WBI Energy Transmission reached a settlement in principle with FERC Trial Staff and all active parties to resolve the rate case. WBI Energy Transmission filed settlement rates to take effect on an interim basis, effective May 1, 2014, pending final approval of the settlement. On June 4, 2014, WBI Energy Transmission submitted to the FERC an Uncontested Offer of Settlement. On June 11, 2014, the Presiding Administrative Law Judge issued a Certification of Uncontested Settlement recommending FERC approval of the settlement without modification. On August 11, 2014, the FERC issued an order approving the settlement without modification and the resulting rates were approved to be effective May 1, 2014. No parties to the proceeding requested rehearing of the order, which is now final. Based on the adjusted base period volumes filed in the case, the annual increase in revenues is approximately $11.5 million.