Regulatory matters	6 Months Ended
Jun. 30, 2017
Regulated Operations [Abstract]
Regulatory matters	Regulatory matters On June 10, 2016, Montana-Dakota filed an application for an increase in electric rates with the WYPSC. Montana-Dakota requested an increase of approximately $3.2 million annually or approximately 13.1 percent above current rates to recover Montana-Dakota's increased investment in facilities along with additional depreciation, operation and maintenance expenses including increased fuel costs, and taxes associated with the increases in investment. On December 28, 2016, Montana-Dakota and the interveners of the case filed a stipulation and agreement reflecting an increase of approximately $2.7 million annually or approximately 11.1 percent above current rates. On April 6, 2017, the WYPSC issued a final order approving the stipulation and agreement with rates effective with service rendered on and after March 1, 2017. On August 12, 2016, Intermountain filed an application with the IPUC for a natural gas rate increase of approximately $10.2 million annually or approximately 4.1 percent above current rates. The request includes rate recovery associated with increased investment in facilities and increased operating expenses. On January 17, 2017, Intermountain provided the IPUC with an updated revenue request of approximately $9.4 million. On April 28, 2017, the IPUC issued an order approving an increase of approximately $4.1 million or approximately 1.6 percent above current rates based on a 9.5 percent return on equity effective with service rendered on and after May 1, 2017. On May 18, 2017, Intermountain filed a petition for reconsideration with the IPUC requesting the reconsideration of certain items denied in the April 28 order. On June 15, 2017, the IPUC granted the request for reconsideration. The IPUC has 13 weeks to complete the reconsideration and until the middle of September 2017 to issue a final order of reconsideration. On December 2, 2016, Montana-Dakota filed an application with the MTPSC requesting authority to implement gas and electric tax tracking adjustments for Montana state and local taxes and fees that reflect the changes in state and local property taxes applicable to natural gas and electric utilities pursuant to Montana law. The requested tax tracking adjustments would result in an increase in revenues of approximately $814,000. On January 17, 2017, the MTPSC issued an order on the tax tracking adjustments. The gas tracking adjustment was approved as an increase to revenues of approximately $474,000 effective January 1, 2017. The electric tax tracking adjustment was approved as an increase to revenues of approximately $251,000 effective May 15, 2017. Montana-Dakota filed a motion for reconsideration of the electric tax tracking adjustment on January 27, 2017. On May 30, 2017, the MTPSC granted Montana-Dakota's motion for reconsideration allowing the full amount of electric taxes covered in the stipulated tariffs to be recovered. The additional revenues of approximately $88,000 will be included in a true-up to be effective in 2018. On December 21, 2016, Great Plains filed an application with the MNPUC requesting authority to implement a natural gas utility infrastructure cost tariff of approximately $456,000 annually effective beginning with service rendered May 20, 2017. The tariff will allow Great Plains to recover infrastructure investments, not previously included in rates, mandated by federal or state agencies associated with Great Plains' pipeline integrity programs. This matter is pending before the MNPUC. On April 1, 2017, Montana-Dakota implemented Phase 2 of the electric rate case approved by the MTPSC on March 25, 2016. The annual increase of $4.7 million is effective with service rendered on and after April 1, 2017. On May 31, 2017, Cascade filed an application with the WUTC for an annual pipeline replacement cost recovery mechanism of approximately $1.6 million or approximately .75 percent of additional revenue. The requested increase includes incremental pipeline replacement investments associated with qualifying pipeline integrity projects. If approved, rates will be effective November 1, 2017. This matter is pending before the WUTC. On June 30, 2017, Montana-Dakota filed an application for advance determination of prudence and a certificate of public convenience and necessity with the NDPSC to purchase an expansion of the Thunder Spirit Wind farm. The advance determination of prudence would provide Montana-Dakota with assurance that the project is prudent and in the best interest of the public and assists in the recovery of Montana-Dakota's investment upon completion of the project. The expansion is expected to serve customers by the end of 2018 and is estimated to cost approximately $85 million. On July 21, 2017, Montana-Dakota filed an application with the NDPSC for a natural gas rate increase of approximately $5.9 million annually or approximately 5.4 percent above current rates. The requested increase is primarily to recover the increased investment in distribution facilities to enhance system safety and reliability and the depreciation and taxes associated with the increase in investment. Montana-Dakota is also introducing a System Safety Integrity Program and the proposed adjustment mechanism required to fund the System Safety Integrity Program. Montana-Dakota has requested an interim increase of approximately $4.6 million or approximately 4.2 percent, subject to refund. This matter is pending before the NDPSC. On July 31, 2017, Cascade filed an application with the WUTC for a natural gas rate increase of approximately $5.9 million annually or approximately 2.7 percent above current rates. The requested increase includes costs associated with increased infrastructure investment and the associated operating expenses. Also included in the request is recovery of operation and maintenance costs associated with a maximum allowable operating pressure validation plan. This matter is pending before the WUTC. Montana-Dakota previously filed an application with the NDPSC on October 14, 2016, for an electric rate increase which also included a requested return on equity to be used in the determination of applications previously filed by Montana-Dakota for a renewable resource cost adjustment rider, an electric generation resource recovery rider, and a transmission cost adjustment rider, as discussed in the following paragraphs. On April 7, 2017, Montana-Dakota, the NDPSC Advocacy Staff and the interveners in the case filed a settlement agreement resolving all issues in the general rate case. The settlement agreement included a net increase of approximately $7.5 million or 3.7 percent above previously approved final rates and a true-up of the return on equity used in the interim renewable resource cost adjustment, the electric generation resource recovery and transmission cost adjustment riders of 9.45 percent; a return on equity of 9.65 percent for base rates and the renewable resource cost adjustment rider on a go-forward basis; and a return on equity of 9.45 percent through December 31, 2019, for the natural gas-fired internal combustion engines and associated facilities included in the electric generation resource recovery rider. A hearing on the settlement agreement was held on April 10, 2017. On June 16, 2017, the NDPSC approved the settlement agreement. On June 26, 2017, Montana-Dakota submitted a compliance filing and on July 14, 2017, submitted updated tariff sheets and a refund plan. The NDPSC approved the compliance filing and refund plan on July 26, 2017, with final rates effective with service rendered on or after August 7, 2017. The final rates are less than the interim rates currently in effect. Therefore, Montana-Dakota will refund the difference to customers, which is approximately 19 percent of the amount collected from the general rate case interim increase, along with refunds to reflect true-ups for the various riders, as applicable. The background information related to the settlement agreement and related applications are discussed in the following paragraphs. On October 26, 2015, Montana-Dakota filed an application with the NDPSC requesting a renewable resource cost adjustment rider for the recovery of the Thunder Spirit Wind project. On January 5, 2016, the NDPSC approved the rider to be effective January 7, 2016, resulting in an annual increase on an interim basis, subject to refund, of $15.1 million based upon a 10.5 percent return on equity to be finalized upon approval of the electric rate case filed on October 14, 2016. The electric rate case settlement agreement filed on April 7, 2017, included a revised return on equity for the rider. The settlement agreement was approved on June 16, 2017, as previously discussed in this note. On October 26, 2015, Montana-Dakota filed an application with the NDPSC for an update to the electric generation resource recovery rider. On March 9, 2016, the NDPSC approved the rider to be effective with service rendered on and after March 15, 2016, which resulted in interim rates, subject to refund, of $9.7 million based upon a 10.5 percent return on equity to be finalized upon the approval of the electric rate case filed on October 14, 2016. The interim rates include recovery of Montana-Dakota's investment in the 88-MW simple-cycle natural gas turbine and associated facilities near Mandan, North Dakota, and the 19 MW of new generation from natural gas-fired internal combustion engines and associated facilities near Sidney, Montana. The electric rate case settlement agreement filed on April 7, 2017, included the net investment authorized for the natural gas-fired internal combustion engines and the return on equity on both investments. The settlement agreement was approved on June 16, 2017, as previously discussed in this note. On November 25, 2015, Montana-Dakota filed an application with the NDPSC for an update of its transmission cost adjustment rider for recovery of MISO-related charges and two transmission projects in North Dakota. On February 10, 2016, the NDPSC approved the transmission cost adjustment effective with service rendered on and after February 12, 2016, resulting in an annual increase on an interim basis, subject to refund, of $6.8 million based upon a 10.5 percent return on equity to be finalized upon approval of the electric rate case filed on October 14, 2016. The electric rate case settlement agreement filed on April 7, 2017, included a revised return on equity for the rider. The settlement agreement was approved on June 16, 2017, as previously discussed in this note. On October 14, 2016, Montana-Dakota filed an application with the NDPSC for an electric rate increase of approximately $13.4 million annually or 6.6 percent above current rates. The request includes rate recovery associated with increased investment in facilities, along with the related depreciation, operation and maintenance expenses and taxes associated with the increased investment. Montana-Dakota requested an interim increase of approximately $13.0 million or approximately 6.5 percent, subject to refund, to be effective within 60 days of the filing. On November 21, 2016, Montana-Dakota filed and on November 30, 2016, the NDPSC approved a revised interim increase of approximately $11.7 million, based on adjustments accepted by the NDPSC, or approximately 5.8 percent above current rates, subject to refund, effective with service rendered on or after December 13, 2016. A settlement agreement was filed on April 7, 2017, and subsequently approved on June 16, 2017, as previously discussed in this note.

Regulatory matters

On June 10, 2016, Montana-Dakota filed an application for an increase in electric rates with the WYPSC. Montana-Dakota requested an increase of approximately $3.2 million annually or approximately 13.1 percent above current rates to recover Montana-Dakota's increased investment in facilities along with additional depreciation, operation and maintenance expenses including increased fuel costs, and taxes associated with the increases in investment. On December 28, 2016, Montana-Dakota and the interveners of the case filed a stipulation and agreement reflecting an increase of approximately $2.7 million annually or approximately 11.1 percent above current rates. On April 6, 2017, the WYPSC issued a final order approving the stipulation and agreement with rates effective with service rendered on and after March 1, 2017.

On August 12, 2016, Intermountain filed an application with the IPUC for a natural gas rate increase of approximately $10.2 million annually or approximately 4.1 percent above current rates. The request includes rate recovery associated with increased investment in facilities and increased operating expenses. On January 17, 2017, Intermountain provided the IPUC with an updated revenue request of approximately $9.4 million. On April 28, 2017, the IPUC issued an order approving an increase of approximately $4.1 million or approximately 1.6 percent above current rates based on a 9.5 percent return on equity effective with service rendered on and after May 1, 2017. On May 18, 2017, Intermountain filed a petition for reconsideration with the IPUC requesting the reconsideration of certain items denied in the April 28 order. On June 15, 2017, the IPUC granted the request for reconsideration. The IPUC has 13 weeks to complete the reconsideration and until the middle of September 2017 to issue a final order of reconsideration.

On December 2, 2016, Montana-Dakota filed an application with the MTPSC requesting authority to implement gas and electric tax tracking adjustments for Montana state and local taxes and fees that reflect the changes in state and local property taxes applicable to natural gas and electric utilities pursuant to Montana law. The requested tax tracking adjustments would result in an increase in revenues of approximately $814,000. On January 17, 2017, the MTPSC issued an order on the tax tracking adjustments. The gas tracking adjustment was approved as an increase to revenues of approximately $474,000 effective January 1, 2017. The electric tax tracking adjustment was approved as an increase to revenues of approximately $251,000 effective May 15, 2017. Montana-Dakota filed a motion for reconsideration of the electric tax tracking adjustment on January 27, 2017. On May 30, 2017, the MTPSC granted Montana-Dakota's motion for reconsideration allowing the full amount of electric taxes covered in the stipulated tariffs to be recovered. The additional revenues of approximately $88,000 will be included in a true-up to be effective in 2018.

On December 21, 2016, Great Plains filed an application with the MNPUC requesting authority to implement a natural gas utility infrastructure cost tariff of approximately $456,000 annually effective beginning with service rendered May 20, 2017. The tariff will allow Great Plains to recover infrastructure investments, not previously included in rates, mandated by federal or state agencies associated with Great Plains' pipeline integrity programs. This matter is pending before the MNPUC.

On April 1, 2017, Montana-Dakota implemented Phase 2 of the electric rate case approved by the MTPSC on March 25, 2016. The annual increase of $4.7 million is effective with service rendered on and after April 1, 2017.

On May 31, 2017, Cascade filed an application with the WUTC for an annual pipeline replacement cost recovery mechanism of approximately $1.6 million or approximately .75 percent of additional revenue. The requested increase includes incremental pipeline replacement investments associated with qualifying pipeline integrity projects. If approved, rates will be effective November 1, 2017. This matter is pending before the WUTC.

On June 30, 2017, Montana-Dakota filed an application for advance determination of prudence and a certificate of public convenience and necessity with the NDPSC to purchase an expansion of the Thunder Spirit Wind farm. The advance determination of prudence would provide Montana-Dakota with assurance that the project is prudent and in the best interest of the public and assists in the recovery of Montana-Dakota's investment upon completion of the project. The expansion is expected to serve customers by the end of 2018 and is estimated to cost approximately $85 million.

On July 21, 2017, Montana-Dakota filed an application with the NDPSC for a natural gas rate increase of approximately $5.9 million annually or approximately 5.4 percent above current rates. The requested increase is primarily to recover the increased investment in distribution facilities to enhance system safety and reliability and the depreciation and taxes associated with the increase in investment. Montana-Dakota is also introducing a System Safety Integrity Program and the proposed adjustment mechanism required to fund the System Safety Integrity Program. Montana-Dakota has requested an interim increase of approximately $4.6 million or approximately 4.2 percent, subject to refund. This matter is pending before the NDPSC.

On July 31, 2017, Cascade filed an application with the WUTC for a natural gas rate increase of approximately $5.9 million annually or approximately 2.7 percent above current rates. The requested increase includes costs associated with increased infrastructure investment and the associated operating expenses. Also included in the request is recovery of operation and maintenance costs associated with a maximum allowable operating pressure validation plan. This matter is pending before the WUTC.

Montana-Dakota previously filed an application with the NDPSC on October 14, 2016, for an electric rate increase which also included a requested return on equity to be used in the determination of applications previously filed by Montana-Dakota for a renewable resource cost adjustment rider, an electric generation resource recovery rider, and a transmission cost adjustment rider, as discussed in the following paragraphs. On April 7, 2017, Montana-Dakota, the NDPSC Advocacy Staff and the interveners in the case filed a settlement agreement resolving all issues in the general rate case. The settlement agreement included a net increase of approximately $7.5 million or 3.7 percent above previously approved final rates and a true-up of the return on equity used in the interim renewable resource cost adjustment, the electric generation resource recovery and transmission cost adjustment riders of 9.45 percent; a return on equity of 9.65 percent for base rates and the renewable resource cost adjustment rider on a go-forward basis; and a return on equity of 9.45 percent through December 31, 2019, for the natural gas-fired internal combustion engines and associated facilities included in the electric generation resource recovery rider. A hearing on the settlement agreement was held on April 10, 2017. On June 16, 2017, the NDPSC approved the settlement agreement. On June 26, 2017, Montana-Dakota submitted a compliance filing and on July 14, 2017, submitted updated tariff sheets and a refund plan. The NDPSC approved the compliance filing and refund plan on July 26, 2017, with final rates effective with service rendered on or after August 7, 2017. The final rates are less than the interim rates currently in effect. Therefore, Montana-Dakota will refund the difference to customers, which is approximately 19 percent of the amount collected from the general rate case interim increase, along with refunds to reflect true-ups for the various riders, as applicable. The background information related to the settlement agreement and related applications are discussed in the following paragraphs.

On October 26, 2015, Montana-Dakota filed an application with the NDPSC requesting a renewable resource cost adjustment rider for the recovery of the Thunder Spirit Wind project. On January 5, 2016, the NDPSC approved the rider to be effective January 7, 2016, resulting in an annual increase on an interim basis, subject to refund, of $15.1 million based upon a 10.5 percent return on equity to be finalized upon approval of the electric rate case filed on October 14, 2016. The electric rate case settlement agreement filed on April 7, 2017, included a revised return on equity for the rider. The settlement agreement was approved on June 16, 2017, as previously discussed in this note.

On October 26, 2015, Montana-Dakota filed an application with the NDPSC for an update to the electric generation resource recovery rider. On March 9, 2016, the NDPSC approved the rider to be effective with service rendered on and after March 15, 2016, which resulted in interim rates, subject to refund, of $9.7 million based upon a 10.5 percent return on equity to be finalized upon the approval of the electric rate case filed on October 14, 2016. The interim rates include recovery of Montana-Dakota's investment in the 88-MW simple-cycle natural gas turbine and associated facilities near Mandan, North Dakota, and the 19 MW of new generation from natural gas-fired internal combustion engines and associated facilities near Sidney, Montana. The electric rate case settlement agreement filed on April 7, 2017, included the net investment authorized for the natural gas-fired internal combustion engines and the return on equity on both investments. The settlement agreement was approved on June 16, 2017, as previously discussed in this note.

On November 25, 2015, Montana-Dakota filed an application with the NDPSC for an update of its transmission cost adjustment rider for recovery of MISO-related charges and two transmission projects in North Dakota. On February 10, 2016, the NDPSC approved the transmission cost adjustment effective with service rendered on and after February 12, 2016, resulting in an annual increase on an interim basis, subject to refund, of $6.8 million based upon a 10.5 percent return on equity to be finalized upon approval of the electric rate case filed on October 14, 2016. The electric rate case settlement agreement filed on April 7, 2017, included a revised return on equity for the rider. The settlement agreement was approved on June 16, 2017, as previously discussed in this note.

On October 14, 2016, Montana-Dakota filed an application with the NDPSC for an electric rate increase of approximately $13.4 million annually or 6.6 percent above current rates. The request includes rate recovery associated with increased investment in facilities, along with the related depreciation, operation and maintenance expenses and taxes associated with the increased investment. Montana-Dakota requested an interim increase of approximately $13.0 million or approximately 6.5 percent, subject to refund, to be effective within 60 days of the filing. On November 21, 2016, Montana-Dakota filed and on November 30, 2016, the NDPSC approved a revised interim increase of approximately $11.7 million, based on adjustments accepted by the NDPSC, or approximately 5.8 percent above current rates, subject to refund, effective with service rendered on or after December 13, 2016. A settlement agreement was filed on April 7, 2017, and subsequently approved on June 16, 2017, as previously discussed in this note.