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Long-term borrowings (Details 4) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 22, 2022	Oct. 13, 2022	Jun. 15, 2022	Mar. 23, 2022	Dec. 31, 2021
Long-term debt outstanding [Line Items]
Long-term debt	$ 2,841,425					$ 2,741,900
Montana-Dakota Utilities Co. [Member]
Long-term debt outstanding [Line Items]
Ratio of total debt to total capitalization	51.00%
Cascade Natural Gas [Member]
Long-term debt outstanding [Line Items]
Ratio of total debt to total capitalization	50.00%
Intermountain Gas Company
Long-term debt outstanding [Line Items]
Ratio of total debt to total capitalization	57.00%
Intermountain Gas Company | Revolving credit facility | Long-term debt
Long-term debt outstanding [Line Items]
Facility limit, maximum borrowing capacity	$ 100,000
Centennial Energy Holdings, Inc.
Long-term debt outstanding [Line Items]
Ratio of total debt to total capitalization	46.00%
WBI Energy Transmission, Inc.
Long-term debt outstanding [Line Items]
Ratio of total debt to total capitalization	40.00%
Senior Notes
Long-term debt outstanding [Line Items]
Long-term debt	$ 2,258,500					$ 2,125,000
Weighted average interest rate	4.32%
Senior Notes | Cascade Natural Gas [Member]
Long-term debt outstanding [Line Items]
Long-term debt				$ 50,000
Weighted average interest rate				4.50%
Ratio of total debt to total capitalization as specified in debt covenants				65.00%
Senior Notes | Intermountain Gas Company
Long-term debt outstanding [Line Items]
Long-term debt				$ 40,000
Weighted average interest rate				4.68%
Ratio of total debt to total capitalization as specified in debt covenants				65.00%
Senior Notes | Centennial Energy Holdings, Inc.
Long-term debt outstanding [Line Items]
Long-term debt					$ 150,000
Weighted average interest rate					3.71%
Ratio of total debt to total capitalization as specified in debt covenants					60.00%
Senior Notes | WBI Energy Transmission, Inc.
Long-term debt outstanding [Line Items]
Long-term debt	$ 235,000	$ 40,000
Weighted average interest rate		6.67%
Ratio of total debt to total capitalization as specified in debt covenants	55.00%
Long-term private shelf agreement issuance capacity		$ 350,000
Remaining capacity under uncommitted private shelf agreement	$ 115,000
Revolving credit facility | Montana-Dakota Utilities Co. [Member]
Long-term debt outstanding [Line Items]
Ratio of funded debt to total capitalization as specified in debt covenants	65.00%
Revolving credit facility | Cascade Natural Gas [Member]
Long-term debt outstanding [Line Items]
Ratio of total debt to total capitalization as specified in debt covenants	65.00%
Revolving credit facility | Intermountain Gas Company
Long-term debt outstanding [Line Items]
Ratio of total debt to total capitalization as specified in debt covenants	65.00%
Facility limit, maximum borrowing capacity			$ 100,000
Revolving credit facility | Centennial Energy Holdings, Inc.
Long-term debt outstanding [Line Items]
Ratio of total debt to total capitalization as specified in debt covenants	65.00%

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