Regulatory Matters (Details)	12 Months Ended
	Dec. 31, 2023 USD ($) Rate
South Dakota
Public Utilities, General Disclosures [Line Items]
Requested Rate base	$ 787,300,000
Electric
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	$ 151,600,000
Electric | Montana
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Return on Equity, Percentage	9.65%
Public Utilities, Approved Equity Capital Structure, Percentage | Rate	48.02%
PCCAM base costs amount	$ 138,700,000
Public Utilities, PCCAM base costs approved through settlement agreement	$ 208,400,000
Electric | South Dakota
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Equity Capital Structure, Percentage | Rate	50.50%
Public Utilities, Approved Equity Capital Structure, Percentage | Rate	50.50%
Public Utilities, Approved Rate of Return | Rate	6.81%
Approved Rate base	$ 791,800,000
Requested Rate of Return | Rate	7.54%
Electric | Base electric rate | Montana
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 67,400,000
Electric | Base electric rate | South Dakota
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	30,900,000
Public Utilities, Approved Rate Increase (Decrease), Amount	21,500,000
Electric | PCCAM base amount | Montana
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	69,700,000
Electric | Electric property tax tracker true-up | Montana
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	14,500,000
Gas Domestic Regulated [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount	$ 18,300,000
Gas Domestic Regulated [Member] | Montana
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Return on Equity, Percentage	9.55%
Public Utilities, Approved Equity Capital Structure, Percentage | Rate	48.02%
Gas Domestic Regulated [Member] | Base natural gas rate | Montana
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 14,100,000
Gas Domestic Regulated [Member] | Natural gas property tax tracker true-up | Montana
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 4,200,000