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Revenue from Contracts with Customers
 6 Months Ended
Jun. 30, 2026
Revenue from Contract with Customer [Abstract]  
Revenue from Contract with Customer [Text Block] Revenue from Contracts with Customers
Nature of Goods and Services

We provide retail electric and natural gas services to three primary customer classes. Our largest customer class consists of residential customers, which includes single private dwellings and individual apartments. Our commercial customers consist primarily of main street businesses, and our industrial customers consist primarily of manufacturing and processing businesses that turn raw materials into products.

Electric Segment - Our regulated electric utility business primarily provides generation, transmission, and distribution services to customers in our Montana and South Dakota jurisdictions. We recognize revenue when electricity is delivered to the customer. Payments on our tariff-based sales are generally due 0-30 days after the billing date.

Natural Gas Segment - Our regulated natural gas utility business primarily provides production, storage, transmission, and distribution services to customers in our Montana, South Dakota, and Nebraska jurisdictions. We recognize revenue when natural gas is delivered to the customer. Payments on our tariff-based sales are generally due 0-30 days after the billing date.

Disaggregation of Revenue

The following tables disaggregate our revenue by major source and customer class (in thousands):

Three Months Ended
June 30, 2026June 30, 2025
ElectricNatural GasTotalElectricNatural GasTotal
Montana$98,447 $19,711 $118,158 $81,824 $17,968 $99,792 
South Dakota17,983 5,776 23,759 16,235 5,566 21,801 
Nebraska— 4,196 4,196 — 4,523 4,523 
Residential116,430 29,683 146,113 98,059 28,057 126,116 
Montana110,833 12,211 123,044 93,910 10,499 104,409 
South Dakota30,341 4,141 34,482 27,737 3,920 31,657 
Nebraska— 1,994 1,994 — 2,346 2,346 
Commercial141,174 18,346 159,520 121,647 16,765 138,412 
Industrial10,831 844 11,675 9,888 144 10,032 
Lighting, governmental, irrigation, and interdepartmental14,144 268 14,412 9,421 270 9,691 
Total Retail Revenues282,579 49,141 331,720 239,015 45,236 284,251 
Regulatory Amortization(3,645)5,925 2,280 10,325 5,189 15,514 
Transmission29,141 — 29,141 28,147 — 28,147 
Transportation, wholesale and other16,179 13,279 29,458 1,981 12,820 14,801 
Total Revenues$324,254 $68,345 $392,599 $279,468 $63,245 $342,713 
Six Months Ended
June 30, 2026June 30, 2025
ElectricNatural GasTotalElectricNatural GasTotal
Montana$218,885 $67,849 $286,734 $196,801 $69,386 $266,187 
South Dakota41,212 20,300 61,512 38,527 21,136 59,663 
Nebraska— 15,357 15,357 — 17,732 17,732 
Residential260,097 103,506 363,603 235,328 108,254 343,582 
Montana217,315 39,088 256,403 190,862 37,257 228,119 
South Dakota61,738 15,895 77,633 57,051 15,095 72,146 
Nebraska— 8,500 8,500 — 9,787 9,787 
Commercial279,053 63,483 342,536 247,913 62,139 310,052 
Industrial22,695 1,635 24,330 19,988 628 20,616 
Lighting, governmental, irrigation, and interdepartmental19,653 792 20,445 14,114 861 14,975 
Total Retail Revenues581,498 169,416 750,914 517,343 171,882 689,225 
Regulatory Amortization6,426 4,924 11,350 38,015 (4,247)33,768 
Transmission60,112 — 60,112 54,703 — 54,703 
Transportation, wholesale and other38,272 29,521 67,793 4,890 26,757 31,647 
Total Revenues$686,308 $203,861 $890,169 $614,951 $194,392 $809,343