Regulatory matters	9 Months Ended
Sep. 30, 2016
Regulated Operations [Abstract]
Regulatory matters	Regulatory matters On June 30, 2015, Montana-Dakota filed an application with the SDPUC for an electric rate increase. Montana-Dakota requested a total increase of approximately $2.7 million annually or approximately 19.2 percent above current rates to recover Montana-Dakota’s investments in modifications to generation facilities to comply with new EPA requirements, the addition and/or replacement of capacity and energy requirements and transmission facilities along with the additional depreciation, operation and maintenance expenses and taxes associated with the increases in investment. An interim increase of $2.7 million, subject to refund, was implemented January 1, 2016. Montana-Dakota and the SDPUC staff filed a settlement stipulation reflecting an overall annual increase of approximately $1.4 million including a transmission cost recovery rider and an infrastructure rider. A settlement hearing was held on June 7, 2016. The SDPUC issued an order approving the settlement on June 15, 2016. The approved rates were effective with service rendered on and after July 1, 2016. The final approved rate increase was less than the interim rate increase implemented January 1, 2016; therefore, Montana-Dakota refunded the difference as bill credits on customer bills in October 2016. On June 30, 2015, Montana-Dakota filed an application for a natural gas rate increase with the SDPUC. Montana-Dakota requested a total increase of approximately $1.5 million annually or approximately 3.1 percent above current rates to recover increased operating expenses along with increased investment in facilities, including the related depreciation expense and taxes, partially offset by an increase in customers and throughput. An interim increase of $1.5 million, subject to refund, was implemented January 1, 2016. Montana-Dakota, the SDPUC staff and other interested parties filed a settlement stipulation reflecting an overall increase of approximately $1.2 million. A settlement hearing was held on June 7, 2016. The SDPUC issued an order approving the settlement on June 15, 2016. The approved rates were effective with service rendered on and after July 1, 2016. The final approved rate increase was less than the interim rate increase implemented January 1, 2016; therefore, Montana-Dakota refunded the difference as bill credits on customer bills in October 2016. On September 30, 2015, Great Plains filed an application for a natural gas rate increase with the MNPUC. Great Plains requested a total increase of approximately $1.6 million annually or approximately 6.4 percent above current rates to recover increased operating expenses along with increased investment in facilities, including the related depreciation expense and taxes. An interim increase of $1.5 million or approximately 6.4 percent, subject to refund, was effective with service rendered on and after January 1, 2016. A technical hearing was held April 7, 2016. The MNPUC issued an order on September 6, 2016, authorizing an increase of approximately $1.1 million annually or approximately 5.2 percent with the requirement that Great Plains submit a compliance filing within 30 days. On September 22, 2016, Great Plains submitted the required compliance filing which included a refund plan to return the amount of interim revenues collected above the final rates. The final rates will be implemented upon approval of the compliance filing by the MNPUC. 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. The interim rate is pending the determination of the return on equity in the general rate case application filed on October 14, 2016, as 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. 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 net investment authorized for the natural gas-fired internal combustion engines and the return on equity on both investments are pending in the general rate case application filed October 14, 2016, as 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 located 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. The interim rate is pending the determination of the return on equity in the general rate case application filed October 14, 2016, as discussed in this note. On December 1, 2015, Cascade filed an application with the WUTC for a natural gas rate increase. Cascade requested a total increase of approximately $10.5 million annually or approximately 4.2 percent above current rates. The requested increase includes rate recovery associated with increased infrastructure investment and the associated operating expenses. On July 7, 2016, the WUTC approved a settlement of $4.0 million annually. The approved rates were effective with service rendered on or after September 1, 2016. On April 29, 2016, Cascade filed an application with the OPUC for a natural gas rate increase of approximately $1.9 million annually or approximately 2.8 percent above current rates. The request includes rate recovery associated with pipeline replacement and improvement projects to ensure the integrity of Cascade's system. On October 6, 2016, Cascade, staff of the OPUC and the interveners in the case filed a stipulation and settlement agreement reflecting an annual increase of approximately $754,000 to be effective March 1, 2017. This matter is pending before the OPUC. On June 1, 2016, Cascade filed an application with the WUTC for an annual pipeline replacement cost recovery mechanism of $4.6 million annually or approximately 2.0 percent of additional revenue. The requested increase includes $2.4 million associated with incremental pipeline replacement investments and $2.2 million for an alternative recovery request of incremental operation and maintenance costs associated with a maximum allowable operating pressure validation plan. On October 17, 2016, Cascade filed an update to the application that reduced the incremental pipeline replacement investment to $1.9 million and removed the operation and maintenance costs associated with a maximum allowable operating pressure validation plan. On October 27, 2016, the WUTC allowed the pipeline replacement cost recovery mechanism to become effective November 1, 2016. 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. A hearing has been scheduled for January 18-19, 2017. This matter is pending before the WYPSC. 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. A hearing has been scheduled for March 1-2, 2017. This matter is pending before the IPUC. 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, subject to refund, to be effective within 60 days of the filing. This matter is pending before the NDPSC.

Regulatory matters

On June 30, 2015, Montana-Dakota filed an application with the SDPUC for an electric rate increase. Montana-Dakota requested a total increase of approximately $2.7 million annually or approximately 19.2 percent above current rates to recover Montana-Dakota’s investments in modifications to generation facilities to comply with new EPA requirements, the addition and/or replacement of capacity and energy requirements and transmission facilities along with the additional depreciation, operation and maintenance expenses and taxes associated with the increases in investment. An interim increase of $2.7 million, subject to refund, was implemented January 1, 2016. Montana-Dakota and the SDPUC staff filed a settlement stipulation reflecting an overall annual increase of approximately $1.4 million including a transmission cost recovery rider and an infrastructure rider. A settlement hearing was held on June 7, 2016. The SDPUC issued an order approving the settlement on June 15, 2016. The approved rates were effective with service rendered on and after July 1, 2016. The final approved rate increase was less than the interim rate increase implemented January 1, 2016; therefore, Montana-Dakota refunded the difference as bill credits on customer bills in October 2016.

On June 30, 2015, Montana-Dakota filed an application for a natural gas rate increase with the SDPUC. Montana-Dakota requested a total increase of approximately $1.5 million annually or approximately 3.1 percent above current rates to recover increased operating expenses along with increased investment in facilities, including the related depreciation expense and taxes, partially offset by an increase in customers and throughput. An interim increase of $1.5 million, subject to refund, was implemented January 1, 2016. Montana-Dakota, the SDPUC staff and other interested parties filed a settlement stipulation reflecting an overall increase of approximately $1.2 million. A settlement hearing was held on June 7, 2016. The SDPUC issued an order approving the settlement on June 15, 2016. The approved rates were effective with service rendered on and after July 1, 2016. The final approved rate increase was less than the interim rate increase implemented January 1, 2016; therefore, Montana-Dakota refunded the difference as bill credits on customer bills in October 2016.

On September 30, 2015, Great Plains filed an application for a natural gas rate increase with the MNPUC. Great Plains requested a total increase of approximately $1.6 million annually or approximately 6.4 percent above current rates to recover increased operating expenses along with increased investment in facilities, including the related depreciation expense and taxes. An interim increase of $1.5 million or approximately 6.4 percent, subject to refund, was effective with service rendered on and after January 1, 2016. A technical hearing was held April 7, 2016. The MNPUC issued an order on September 6, 2016, authorizing an increase of approximately $1.1 million annually or approximately 5.2 percent with the requirement that Great Plains submit a compliance filing within 30 days. On September 22, 2016, Great Plains submitted the required compliance filing which included a refund plan to return the amount of interim revenues collected above the final rates. The final rates will be implemented upon approval of the compliance filing by the MNPUC.

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. The interim rate is pending the determination of the return on equity in the general rate case application filed on October 14, 2016, as 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. 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 net investment authorized for the natural gas-fired internal combustion engines and the return on equity on both investments are pending in the general rate case application filed October 14, 2016, as 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 located 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. The interim rate is pending the determination of the return on equity in the general rate case application filed October 14, 2016, as discussed in this note.

On December 1, 2015, Cascade filed an application with the WUTC for a natural gas rate increase. Cascade requested a total increase of approximately $10.5 million annually or approximately 4.2 percent above current rates. The requested increase includes rate recovery associated with increased infrastructure investment and the associated operating expenses. On July 7, 2016, the WUTC approved a settlement of $4.0 million annually. The approved rates were effective with service rendered on or after September 1, 2016.

On April 29, 2016, Cascade filed an application with the OPUC for a natural gas rate increase of approximately $1.9 million annually or approximately 2.8 percent above current rates. The request includes rate recovery associated with pipeline replacement and improvement projects to ensure the integrity of Cascade's system. On October 6, 2016, Cascade, staff of the OPUC and the interveners in the case filed a stipulation and settlement agreement reflecting an annual increase of approximately $754,000 to be effective March 1, 2017. This matter is pending before the OPUC.

On June 1, 2016, Cascade filed an application with the WUTC for an annual pipeline replacement cost recovery mechanism of $4.6 million annually or approximately 2.0 percent of additional revenue. The requested increase includes $2.4 million associated with incremental pipeline replacement investments and $2.2 million for an alternative recovery request of incremental operation and maintenance costs associated with a maximum allowable operating pressure validation plan. On October 17, 2016, Cascade filed an update to the application that reduced the incremental pipeline replacement investment to $1.9 million and removed the operation and maintenance costs associated with a maximum allowable operating pressure validation plan. On October 27, 2016, the WUTC allowed the pipeline replacement cost recovery mechanism to become effective November 1, 2016.

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. A hearing has been scheduled for January 18-19, 2017. This matter is pending before the WYPSC.

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. A hearing has been scheduled for March 1-2, 2017. This matter is pending before the IPUC.

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, subject to refund, to be effective within 60 days of the filing. This matter is pending before the NDPSC.