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Regulatory matters
 9 Months Ended
Sep. 30, 2025
Regulated Operations [Abstract]  
Regulatory matters Regulatory matters
The Company regularly reviews the need for electric and natural gas rate changes in each of the jurisdictions in which service is provided. The Company files for rate adjustments to seek recovery of operating costs and capital investments, as well as reasonable returns as allowed by regulators. Certain regulatory proceedings and cases may also contain recurring mechanisms that can have an annual true-up. Examples of these recurring mechanisms include: infrastructure riders, transmission trackers, renewable resource cost adjustment riders, as well as weather normalization and decoupling mechanisms. The following paragraphs summarize the Company's significant open regulatory proceedings and cases by jurisdiction including updates to those reported in the 2024 Annual Report and should be read in conjunction with previous filings. The Company is unable to predict the ultimate outcome of these matters, the timing of final decisions of the various regulators and courts, or the effect on the Company's results of operations, financial position or cash flows.
IPUC
On May 30, 2025, Intermountain filed a request with the IPUC for a natural gas general rate increase of approximately $26.5 million annually or 8.6 percent above current rates. The requested increase is primarily to recover increased operating expenses and costs associated with plant additions, as well as revenues necessary to produce a fair rate of return to enable continued safe and reliable service. On October 20, 2025, an all-party settlement agreement was filed reflecting an annual revenue increase of $13.0 million or 4.2 percent. The IPUC has a hearing scheduled November 18 and 19, 2025, with rates expected to be effective January 1, 2026. The reduction from the original filing is largely related to a lower return on equity, a monthly average rate base methodology versus end of period, and reduced incentives.
NDPSC
On July 15, 2025, Montana-Dakota filed an annual update to its transmission cost adjustment rider with the NDPSC requesting to recover revenues of approximately $6.3 million, which includes a true-up of the prior period adjustment, resulting in an increase of approximately $7.2 million over current rates. Included in this filing is capital investment in transmission projects and the associated revenue of approximately $8.6 million. On October 23, 2025, the NDPSC approved the transmission cost adjustment with rates effective November 1, 2025.
Montana-Dakota has a renewable resource cost adjustment rate tariff that allows for annual adjustments for recent projected capital costs and related expenses for projects determined to be recoverable under the tariff. On October 31, 2025, Montana-Dakota filed an annual update to its renewable resource cost adjustment, including Badger Wind, requesting to recover a revenue requirement of approximately $43.6 million annually. The update reflects an increase of approximately $25.3 million annually from the revenues currently included in rates.
MTPSC
On July 15, 2024, Montana-Dakota filed a request with the MTPSC for a natural gas general rate increase of approximately $9.4 million annually or 11.1 percent above current rates. The requested increase is primarily to recover investments in system upgrades and pipeline replacement projects enhancing the reliability, safety and integrity of the natural gas system, as well as increased costs to operate and maintain that system. On October 15, 2024, the MTPSC denied Montana-Dakota's request for an interim rate increase of approximately $8.0 million annually or 10.2 percent above current rates. On October 25, 2024, Montana-Dakota filed a motion for reconsideration of the interim rate increase. On January 14, 2025, the MTPSC approved an interim increase of approximately $7.7 million with interim rates effective on and after February 1, 2025. On April 3, 2025, an all-party settlement agreement was filed reflecting an annual revenue increase of $7.3 million or 8.6 percent overall. On October 7, 2025, the MTPSC approved the settlement with rates effective November 1, 2025.
On September 30, 2025, Montana-Dakota filed a request with the MTPSC for an electric general rate increase of approximately $14.1 million annually or 20.2 percent above current rates. The requested increase is primarily to recover investments, including Badger Wind, made since the last regulatory procedure, the corresponding depreciation on those investments and increased operation and maintenance expenses. The filing includes a request for a Systems Management Cost Adjustment mechanism for cost recovery of transmission and wildfire related costs. This matter is pending before the MTPSC.
SDPUC
Montana-Dakota has an infrastructure rider that allows annual adjustments for recent projected capital costs and related expense for projects determined to be recoverable under the tariff. On October 31, Montana-Dakota filed an annual update to its infrastructure rider, including Badger Wind, requesting to recover a revenue requirement of approximately $1.5 million annually. The update reflects an increase of $1.1 million annually from the revenues currently included in rates.
WYPSC
On June 30, 2025, Montana-Dakota filed a request with the WYPSC for an electric general rate increase of approximately $7.5 million annually or 24.4 percent above current rates. The filing includes a request for a Reliability and Safety Infrastructure Rider. The requested increase is primarily to recover increases in operation and maintenance expenses, investments made since the last rate case, and the corresponding depreciation on those infrastructure investments. This matter is pending before the WYPSC.
On August 15, 2025, Montana-Dakota filed for approval with the WYPSC a gas System Safety and Integrity Rider. The System Safety Integrity Rider would allow Montana-Dakota to recover costs and expenses associated with a pipeline replacement program.