SDPUC (Details 4) - SDPUC - Montana-Dakota Utilities Co. [Member] - USD ($)	May 01, 2021	Mar. 11, 2021
Electricity [Member] | Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Total Transmission Cost Adjustment Rider	$ 1,000,000.0
Transmission Capital Projects Increase (Decrease)	274,000
Total Infrastructure Rider	1,000,000.0
Public Utilities, Approved Rate Increase (Decrease), Amount	(236,000)
Gas Distribution [Member] | Subsequent Event [Member]
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount	$ 5,500,000
Pending Rate Case [Member] | Electricity [Member]
Public Utilities, General Disclosures [Line Items]
Total Infrastructure Rider		$ 0