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Regulatory Matters: Winter Storm Uri (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Feb. 24, 2021	Dec. 31, 2020
Public Utilities, General Disclosures [Line Items]
Regulatory assets	$ 802,257		$ 278,258
Winter Storm Uri Incremental Costs in a Separately Tracked Mechanism
Public Utilities, General Disclosures [Line Items]
Regulatory assets	480,842		0
Deferred energy and gas costs
Public Utilities, General Disclosures [Line Items]
Regulatory assets	68,402		39,035
Deferred gas cost adjustments
Public Utilities, General Disclosures [Line Items]
Regulatory assets	17,066		$ 3,200
Senior Unsecured Notes Due 2021
Public Utilities, General Disclosures [Line Items]
Debt Instrument, Face Amount		$ 800,000
Winter Storm Uri
Public Utilities, General Disclosures [Line Items]
Incremental Fuel, Purchased Power and Natural Gas Costs	571,000
Regulatory assets	558,825
Income Statement Impacts	12,500
Winter Storm Uri | Winter Storm Uri Incremental Costs in a Separately Tracked Mechanism
Public Utilities, General Disclosures [Line Items]
Regulatory assets	480,842
Winter Storm Uri | Deferred energy and gas costs
Public Utilities, General Disclosures [Line Items]
Regulatory assets	27,166
Winter Storm Uri | Deferred gas cost adjustments
Public Utilities, General Disclosures [Line Items]
Regulatory assets	50,817
Winter Storm Uri | Interest expense incurred net of amounts capitalized (including amortization of debt issuance costs, premiums and discounts)
Public Utilities, General Disclosures [Line Items]
Income Statement Impacts	700
Winter Storm Uri | Electric Utilities
Public Utilities, General Disclosures [Line Items]
Regulatory assets	50,966
Winter Storm Uri | Electric Utilities | Wholesale Power Margin Impacts
Public Utilities, General Disclosures [Line Items]
Income Statement Impacts	3,200
Winter Storm Uri | Electric Utilities | Non-recoverable Fuel Costs
Public Utilities, General Disclosures [Line Items]
Income Statement Impacts	2,100
Winter Storm Uri | Electric Utilities | Colorado Electric
Public Utilities, General Disclosures [Line Items]
Regulatory assets	25,500
Winter Storm Uri | Electric Utilities | South Dakota Electric
Public Utilities, General Disclosures [Line Items]
Regulatory assets	22,200
Winter Storm Uri | Electric Utilities | Wyoming Electric
Public Utilities, General Disclosures [Line Items]
Regulatory assets	3,266
Winter Storm Uri | Gas Utilities
Public Utilities, General Disclosures [Line Items]
Regulatory assets	507,859
Winter Storm Uri | Gas Utilities | Arkansas Gas
Public Utilities, General Disclosures [Line Items]
Regulatory assets	137,500
Winter Storm Uri | Gas Utilities | Colorado Gas
Public Utilities, General Disclosures [Line Items]
Regulatory assets	77,850
Winter Storm Uri | Gas Utilities | Iowa Gas
Public Utilities, General Disclosures [Line Items]
Regulatory assets	95,450
Winter Storm Uri | Gas Utilities | Kansas Gas
Public Utilities, General Disclosures [Line Items]
Regulatory assets	87,900
Winter Storm Uri | Gas Utilities | Nebraska Gas
Public Utilities, General Disclosures [Line Items]
Regulatory assets	79,750
Winter Storm Uri | Gas Utilities | Wyoming Gas
Public Utilities, General Disclosures [Line Items]
Regulatory assets	29,409
Winter Storm Uri | Gas Utilities | Black Hills Energy Services | Non-recoverable Fuel Costs
Public Utilities, General Disclosures [Line Items]
Income Statement Impacts	8,200
Winter Storm Uri | Power Generation | Operating Income (Loss)
Public Utilities, General Disclosures [Line Items]
Income Statement Impacts	$ (1,700)

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