Position [Axis] Position [Axis] Hedging Designation [Domain] Hedging Designation [Domain] Supplemental cash flow information: Supplemental Cash Flow Information [Abstract] Colorado Electric and Nebraska Gas Colorado Electric and Nebraska Gas [Member] Colorado Electric and Nebraska Gas Customer [Domain] Customer [Domain] Selected Balance Sheet Information [Abstract] Selected Balance Sheet Information [Abstract] Selected Balance Sheet Information [Abstract] Letter of Credit Letter of Credit [Member] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Net income available for common stock Net income available for common stock Net Income (Loss) Attributable to Parent Entity Emerging Growth Company Entity Emerging Growth Company Kansas Corporation Commission (KCC) Kansas Corporation Commission (KCC) [Member] Kansas Corporation Commission (KCC) Contract or notional amounts and terms of marketing activities and derivative commodity instruments Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block] Unrecorded Unconditional Purchase Obligation [Table] Unrecorded Unconditional Purchase Obligation [Table] Accrued employee compensation, benefits and withholdings Employee-related Liabilities, Current Interest cost Defined Benefit Plan, Interest Cost Payment for Pension and Other Postretirement Benefits [Abstract] Payment for Pension and Other Postretirement Benefits [Abstract] Income Statement Location [Axis] Income Statement Location [Axis] Iowa Utilities Board (IUB) Iowa Utilities Board (IUB) [Member] Iowa Utilities Board (IUB) Statistical Measurement [Domain] Statistical Measurement [Domain] Entity Address, Address Line One Entity Address, Address Line One Derivative Liabilities, Fair Value Disclosure Derivative Liability Segment Reporting Segment Reporting, Policy [Policy Text Block] Schedule Of Regulatory Assets And Liabilities [Line Items] Schedule Of Regulatory Assets And Liabilities [Line Items] Schedule of regulatory asset and liabilities line items Dividends on common stock Dividends, Common Stock, Cash Mining Mining [Member] Mining Revenue from Contract with Customer [Abstract] Revenue from Contract with Customer [Abstract] Entity Filer Category Entity Filer Category Regulatory Agency [Domain] Regulatory Agency [Domain] Public Utilities, Approved Return on Equity, Percentage Public Utilities, Approved Return on Equity, Percentage Other assets, non-current Other Assets, Noncurrent Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] Senior Unsecured Notes Due 2021 Senior Unsecured Notes Due 2021 [Member] Senior Unsecured Notes Due 2021 Expected return on plan assets Defined Benefit Plan, Expected Return (Loss) on Plan Assets Segments [Axis] Segments [Axis] Non-controlling interest Noncontrolling Interest in Variable Interest Entity Retirement Benefits [Abstract] Retirement Benefits [Abstract] Public Utilities, Term Extension of System Safety and Integrity Rider Public Utilities, Term Extension of System Safety and Integrity Rider Public Utilities, Term Extension of System Safety and Integrity Rider Energy [Domain] Energy [Domain] Transmission/Other Transmission/Other [Member] Transmission/Other [Member] Reclassification Out of Accumulated Other Comprehensive Income (Loss) Reclassification out of Accumulated Other Comprehensive Income [Table Text Block] Operations and maintenance Operating Expense, Maintenance, Operations, and Other Costs and Expense Amount of operating expenses for the period including selling, general, and administrative expenses, costs include routine repairs and maintenance and operations. 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Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Prior service cost (benefit) Defined Benefit Plan, Amortization of Prior Service Cost (Credit) Accrued property, plant and equipment purchases at September 30 Capital Expenditures Incurred but Not yet Paid Fuel, purchased power and cost of natural gas sold Fuel, Purchased Power and Cost of Gas Sold Fuel costs incurred that are directly related to goods produced and sold and services rendered during the reporting period, combined with the amount of purchased power charged against earnings for the period, and cost of gas sold to customers for the period. 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The regulatory treatment under flow-through accounting was applied for this tax benefit generated by utility costs that were previously capitalized for tax purposes in a rate case settlement and resulted in a lower rate increase. A regulatory asset was established to reflect the future increase in taxes payable recovered from sutomers as the temporarty difference reverses.[Member] Document Transition Report Document Transition Report Income Tax Disclosure [Abstract] Income Tax Disclosure [Abstract] Settlement agreement reached with CPUC Staff and various intervenors, subject to the review and approval by an Administrative Law Judge and the CPUC. Settlement agreement reached with CPUC Staff and various intervenors, subject to the review and approval by an Administrative Law Judge and the CPUC. [Member] Settlement agreement reached with CPUC Staff and various intervenors, subject to the review and approval by an Administrative Law Judge and the CPUC. Base Rate Base Rate [Member] TOTAL LIABILITIES AND TOTAL EQUITY Liabilities and Equity Other (none of which is individually significant) Other Accrued Liabilities, Current Public Utilities, General Disclosures [Line Items] Public Utilities, General Disclosures [Line Items] Impairment of investment Impairment of investment Other Asset Impairment Charges Additional paid-in capital Additional Paid in Capital Consolidated Indebtedness to Capitalization Ratio Debt Instrument, Consolidated Indebtedness To Capitalization Ratio Requirement For The Next Fiscal Year Debt Instrument, Consolidated Indebtedness To Capitalization Ratio Requirement For The Next Fiscal Year LIABILITIES AND EQUITY Liabilities and Equity [Abstract] Derivative [Line Items] Derivative [Line Items] Hedging Relationship [Domain] Hedging Relationship [Domain] Interest rate swaps Interest Rate Swaps Interest Rate Swap [Member] Short-term Debt, Type [Domain] Short-term Debt, Type [Domain] Earnings Per Share Earnings Per Share [Text Block] Timing of Transfer of Good or Service [Domain] Timing of Transfer of Good or Service [Domain] Derivative liabilities, current Derivative Liability, Current Operating expenses: Operating Expenses [Abstract] Regulatory liabilities Regulatory Liabilities Regulatory Liabilities Electric wholesale contracts Energy Related Derivative [Member] Income tax receivable, net Income Taxes Receivable, Current Other operating activities, net Increase (Decrease) in Other Operating Assets and Liabilities, Net Balance Sheet Location [Domain] Balance Sheet Location [Domain] Derivative Liabilities, Total Financial and Nonfinancial Liabilities, Fair Value Disclosure Income before Income Taxes Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest Debt Issuance Costs, Net Debt Issuance Costs, Net Natural gas physical contracts, net Natural Gas Physical Purchases [Member] Natural Gas Physical Purchases [Member] Settlement of Plan to Provide TCJA and State Tax Reform benefits to Customers Annually Settlement of Plan to Provide TCJA and State Tax Reform benefits to Customers Annually Settlement of Plan to Provide TCJA and State Tax Reform benefits to Customers Annually Settlement of plan to provide TCJA-related customer billing credits to its customers Settlement of plan to provide TCJA-related customer billing credits to its customers Settlement of plan to provide TCJA-related customer billing credits to its customers. The billing credits, which represent a disposition of excess deferred income tax benefits resulting from the TCJA, will be delivered to customers in the next fiscal year. Kansas Gas Black Hills Energy, Kansas Gas [Member] Black Hills Energy, Kansas Gas Derivative assets, current Derivative Asset, Current Cumulative Effect, Period of Adoption [Axis] Cumulative Effect, Period of Adoption [Axis] Other assets: Other Assets, Noncurrent [Abstract] Trading Symbol Trading Symbol Interest Rate Swap and Commodity Derivative Interest Rate Swap and Commodity Derivative [Member] Interest Rate Swap and Commodity Derivative Approval Recevied from Regulatory Agency Approval Received from Regulatory Agency [Member] Approval Received from Regulatory Agency Current liabilities: Liabilities, Current [Abstract] AOCI Attributable to Parent, Net of Tax [Roll Forward] Accumulated Other Comprehensive Income [Roll Forward] Accumulated Other Comprehensive Income [Roll Forward] Issuance of common stock Stock Issued During Period, Value, New Issues Revenue Recognition Revenue [Policy Text Block] Financing Debt Disclosure [Text Block] Line of Credit Line of Credit [Member] Fair Value, Inputs, Level 3 Fair Value, Inputs, Level 3 [Member] Supplemental Non-qualified Defined Benefit and Defined Contribution Plans Supplemental Employee Retirement Plan [Member] Derivative Instrument [Axis] Derivative Instrument [Axis] Issuance of common stock (in shares) Stock Issued During Period, Shares, New Issues Senior Unsecured Notes Due 2024 Senior Unsecured Notes Due 2024 [Member] Senior Unsecured Notes Due 2024 Gas supply contract termination Gas Supply Contract Termination [Member] Gas Supply Contract Termination [Member] Letters of Credit Letters of Credit Outstanding, Amount Public Utilities, Regulatory Proceeding [Domain] Public Utilities, Regulatory Proceeding [Domain] Winter Storm Uri Incremental Costs in a Separately Tracked Mechanism Storm Costs [Member] Common stock $1 par value; 100,000,000 shares authorized; issued 63,865,151 and 62,827,179 shares, respectively Common Stock, Value, Issued Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Net borrowings (payments) of Revolving Credit Facility and CP Program Net (payments) borrowings of Revolving Credit Facility and Commercial Paper Program Net (payments) borrowings of Revolving Credit Facility and Commercial Paper Program Total other income (expense) Nonoperating Income (Expense) Number Of One Year Extension Options Number Of One Year Extension Options Number Of One Year Extension Options Colorado Electric Colorado Electric [Member] Colorado Electric Net change in cash, restricted cash and cash equivalents Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect Other Postretirement Benefits Plan Other Postretirement Benefits Plan [Member] Public Utilities, Approved Rate Increase (Decrease), Amount Public Utilities, Approved Rate Increase (Decrease), Amount Commitments, contingencies and guarantees (Note 3) Commitments and Contingencies Accumulated other comprehensive income (loss) Accumulated Other Comprehensive Income (Loss), Net of Tax, Period Start Accumulated Other Comprehensive Income (Loss), Net of Tax, Period End Accumulated Other Comprehensive Income (Loss), Net of Tax Fair Value, by Balance Sheet Grouping Fair Value, by Balance Sheet Grouping [Table Text Block] Number of Years TCJA and State Tax Reform Benefits to be Provide to Customers Number of Years TCJA and State Tax Reform Benefits to be Provide to Customers Number of Years TCJA and State Tax Reform Benefits to be Provided to Customers Less: Allowance for doubtful accounts Balance at Beginning of Year Balance at End of Year Accounts Receivable, Allowance for Credit Loss, Current Restricted Stock (in shares) Restricted Stock [Member] Reclassification out of Accumulated Other Comprehensive Income [Axis] Reclassification out of Accumulated Other Comprehensive Income [Axis] Natural gas over-the-counter swaps, net Fixed for Float Swaps Purchased [Member] Fixed for Float Swaps Purchased [Member] Other revenues Other revenues Other [Member] Other [Member] ContractSubjecttoMasterNetting ContractSubjecttoMasterNetting [Member] ContractSubjecttoMasterNetting Antidilutive Securities, Name [Domain] Antidilutive Securities, Name [Domain] Document Period End Date Document Period End Date Equity compensation (in shares) Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements Other Comprehensive Income (Loss), before Reclassifications, Net of Tax Other Comprehensive Income (Loss), before Reclassifications, Net of Tax Reclassification adjustments of benefit plan liability - prior service cost (net of tax of $6, $6, $21 and $19, respectively) Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, after Tax Entity Registrant Name Entity Registrant Name Treasury stock, shares Treasury Stock, Shares Interest expense, net Interest Income (Expense), Net (Tax) benefit on benefit plan liability adjustments - net gain (loss) Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, Tax Interest expense incurred net of amounts capitalized (including amortization of debt issuance costs, premiums and discounts) Interest Expense Interest Costs Incurred Netting Contract Category [Domain] Netting Contract Category [Domain] Netting Contract Category [Domain] Unbilled revenue Unbilled Receivables, Current Electricity Electricity [Member] Derivative liabilities — current Derivative Liabilities, Current [Member] Line item in the statement of financial position in a classified presentation in which the fair value amounts of the derivative instruments are included. 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Operating income Operating income Operating Income (Loss) Regulatory liabilities, non-current Regulatory Liability, Noncurrent Regulatory Asset [Axis] Regulatory Asset [Axis] Regulatory assets Increase (Decrease) in Other Regulatory Assets TC Colorado Solar, LLC TC Colorado Solar, LLC [Member] TC Colorado Solar, LLC Management's Statement Organization, Consolidation, Basis of Presentation, Business Description and Accounting Policies [Text Block] Hedging Designation [Axis] Hedging Designation [Axis] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Stock compensation Share-based Payment Arrangement, Noncash Expense Variable Rate [Domain] Variable Rate [Domain] Additional Paid-in Capital Additional Paid-in Capital [Member] Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Regulatory assets Regulatory assets Regulatory assets Regulatory Assets Dividends on common stock (usd per share) Common Stock, Dividends, Per Share, Cash Paid Treasury Stock Treasury Stock [Member] Wind Assets Wind Assets [Member] Wind Assets Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member] Regulatory Asset, Amortization Period Regulatory Asset, Amortization Period Gas Utilities Gas Utilities [Member] Gas Utilities [Member] Other income (expense), net Other Nonoperating Income (Expense) Long-term Debt, Fair Value Long-term Debt, Fair Value Other investing activities Payments for (Proceeds from) Other Investing Activities Property, plant and equipment additions Payments to Acquire Property, Plant, and Equipment Contributions by Employer Defined Benefit Plan, Plan Assets, Contributions by Employer Maximum Maximum [Member] Line of Credit Facility, Interest Rate at Period End Line of Credit Facility, Interest Rate at Period End Electric Utilities Electric Utilities [Member] Electric Utilities Segment [Member] Total other assets, non-current Assets, Noncurrent, Other than Noncurrent Investments and Property, Plant and Equipment Power Generation Power Generation [Member] Power Generation Legal Entity [Axis] Legal Entity [Axis] Payment for Debt Extinguishment or Debt Prepayment Cost Payment for Debt Extinguishment or Debt Prepayment Cost Accrued Liabilities Schedule Schedule of Accrued Liabilities [Table Text Block] Financing activities: Net Cash Provided by (Used in) Financing Activities [Abstract] At The Market Equity Program Proceeds from Sale of Stock At The Market Equity Program Proceeds from Sale of Stock At The Market Equity Program Proceeds from Sale of Stock Consolidation Items [Axis] Consolidation Items [Axis] Deferred taxes on AFUDC Allowance For Funds Used During Construction [Member] The offsetting entry to other income when an enterprise capitalizes, as part of the cost of plant and equipment, the cost of financing construction as financed partially by equity. Total stockholders’ equity Stockholders' Equity Attributable to Parent Common stock, shares, issued Common Stock, Shares, Issued Designated as Hedging Instrument Designated as Hedging Instrument [Member] Iowa Gas Black Hills energy, Iowa Gas [Member] Black Hills energy, Iowa Gas Public Utilities, Regulatory Proceeding [Axis] Public Utilities, Regulatory Proceeding [Axis] Eurodollar Eurodollar [Member] Equity: Stockholders' Equity Attributable to Parent [Abstract] Schedule of Accumulated Other Comprehensive Income (Loss) Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Retirement Plan Type [Axis] Retirement Plan Type [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Other Comprehensive Income Comprehensive Income (Loss) Note [Text Block] Schedule of Short-term Debt [Table] Schedule of Short-term Debt [Table] Excess deferred income taxes Deferred Income Tax Charges a [Member] Rate Action of a regulator resulting in capitalization or accrual of income taxes Measurement Frequency [Domain] Measurement Frequency [Domain] Debt Instrument, Face Amount Debt Instrument, Face Amount Short-term interest rate Short-term Debt, Weighted Average Interest Rate, at Point in Time Segment Reporting Information, Additional Information [Abstract] Segment Reporting Information, Additional Information [Abstract] Net periodic benefit cost Defined Benefit Plan, Net Periodic Benefit Cost (Credit) City Area Code City Area Code Gas price derivatives Price Risk Derivative [Member] Retained earnings Retained Earnings (Accumulated Deficit) Schedule of Defined Benefit Plans Disclosures [Table] Schedule of Defined Benefit Plans Disclosures [Table] Equity compensation - 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issuances Proceeds from Issuance of Long-term Debt Equity Components [Axis] Equity Components [Axis] Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Retail - Electric , Natural Gas and Coal Retail - Electric , Natural Gas and Coal [Member] Retail - Electric , Natural Gas and Coal Fair Value Disclosures [Abstract] Fair Value Disclosures [Abstract] Antidilutive Securities [Axis] Antidilutive Securities [Axis] Total current assets Assets, Current Cash Flow Hedging Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Other regulatory liabilities Other Regulatory Liabilities [Member] Other regulatory liabilities [Member] Materials, supplies and fuel Total materials, supplies and fuel Inventory, Net Reclassification of net realized (gains) losses on settled/amortized derivatives, net of tax Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax Schedule of Segment Reporting Information, by Segment Schedule of Segment Reporting Information, by Segment [Table Text Block] Services transferred over time Transferred over Time [Member] Entity File Number Entity File Number Colorado Gas Black Hills Energy, Colorado Gas [Member] Black Hills Energy, Colorado Gas [Member] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Condensed Statement of Comprehensive Income [Table] Condensed Statement of Comprehensive Income [Table] Current maturities of long-term debt Long-term Debt, Current Maturities Product and Service [Axis] Product and Service [Axis] Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Deferred gas cost adjustments Asset Recoverable Gas Costs [Member] Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Entity Small Business Entity Small Business Accounts receivable and other current assets Increase (Decrease) in Accounts Receivable and Other Operating Assets Winter Storm Uri Winter Storm Uri [Member] Winter Storm Uri Segment Reporting, Asset Reconciling Item [Line Items] Segment Reporting, Asset Reconciling Item [Line Items] Effective Income Tax Reconciliation, Tax Flow-through Benefit from Repairs and Indirect Costs Effective Income Tax Reconciliation, Tax Flow-through Benefit from Repairs and Indirect Costs Effective Income Tax Reconciliation, Tax Flow-through Benefit from Repairs and Indirect Costs Effective Income Tax Rate Reconciliation Tax Cuts And Jobs Act Of 2017 Amount, Tax Benefit from Bill Credit Effective Income Tax Rate Reconciliation Tax Cuts And Jobs Act Of 2017 Amount, Tax Benefit from Bill Credit Effective Income Tax Rate Reconciliation Tax Cuts And Jobs Act Of 2017 Amount, Tax Benefit from Bill Credit At The Market Equity Offering Program Shares Issued At The Market Equity Offering Program Shares Issued At The Market Equity Offering Program Shares Issued Equity Component [Domain] Equity Component [Domain] Share-based compensation (in shares) Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture Other Stockholders' Equity, Other Carrrying Costs Carrying Costs [Member] Carrying Costs Statement [Line Items] Statement [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Share-based compensation Shares Issued, Value, Share-based Payment Arrangement, after Forfeiture Retirement Plan Type [Domain] Retirement Plan Type [Domain] Short-term Debt, Type [Axis] Short-term Debt, Type [Axis] Regulatory assets Net Regulatory Assets [Abstract] Schedule of Regulatory Assets and Liabilities Schedule of Regulatory Assets and Liabilities [Table Text Block] The entire disclosure for detailed information about regulatory assets and liabilities, including current and noncurrent assets created when regulatory agencies permit the deferral of costs to the balance sheet that would otherwise be required to appear on the company's income statement and would be charged against current expenses or revenues, as well as current and noncurrent liabilities created when regulatory agencies permit. [Table Text Block] Customer deposits and prepayments Customer Deposits and Prepayments Accrued Liabilities - Customer Deposits and Prepayments Contributions to defined benefit pension plans Increase (Decrease) in Obligation, Pension and Other Postretirement Benefits Debt Disclosure [Abstract] Debt Disclosure [Abstract] Fair Value Measurement Fair Value Measurement and Measurement Inputs, Recurring and Nonrecurring [Text Block] Entity Address, State or Province Entity Address, State or Province Income before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Fair Value, Inputs, Level 2 Fair Value, Inputs, Level 2 [Member] Corporate Corporate, Non-Segment [Member] Derivative, Gain (Loss) on Derivative, Net Derivative, Gain (Loss) on Derivative, Net Entity [Domain] Entity [Domain] Customer [Axis] Customer [Axis] Commodity Contract Commodity Contract [Member] Employee Benefit Plans Retirement Benefits [Text Block] Use of Estimates and Basis of Presentation Use of Estimates, Policy [Policy Text Block] Schedule of Earnings Per Share Reconciliation Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Public Utilities, Approved Equity Capital Structure, Percentage Public Utilities, Approved Equity Capital Structure, Percentage Entity Shell Company Entity Shell Company Local Phone Number Local Phone Number Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months Effective Income Tax Rate Reconciliation, Deduction, Qualified Production Activity, Amount Effective Income Tax Rate Reconciliation, Deduction, Qualified Production Activity, Amount Common stock issued Proceeds from Issuance of Common Stock TOTAL ASSETS Assets Assets Distributions to non-controlling interest Payments to Noncontrolling Interests Common stock, shares authorized Common Stock, Shares Authorized Decommissioning costs Environmental Restoration Costs [Member] Interest, net of amounts capitalized Interest Paid, Excluding Capitalized Interest, Operating Activities Ratio of Indebtedness to Net Capital Ratio of Indebtedness to Net Capital Number of Megawatts Capacity Purchased Number of Megawatts Capacity Purchased Number of Megawatts Capacity Purchased Product and Service [Domain] Product and Service [Domain] Nebraska Publc Service Commission (NPSC) Nebraska Publc Service Commission (NPSC) [Member] Nebraska Publc Service Commission (NPSC) Noncontrolling Interest Noncontrolling Interest [Member] Selected Balance Sheet Information Supplemental Balance Sheet Disclosures [Text Block] Deferred energy and fuel cost adjustments Deferred energy and gas costs Deferred Fuel Costs [Member] Account Receivable Schedule Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block] Debt Instrument, Interest Rate, Stated Percentage Debt Instrument, Interest Rate, Stated Percentage Derivative Contract [Domain] Derivative Contract [Domain] Net income attributable to non-controlling interest Net Income (Loss) Attributable to Noncontrolling Interest Revolving Credit Facility Revolving Credit Facility [Member] Cumulative Effect, Period of Adoption [Domain] Cumulative Effect, Period of Adoption [Domain] Measurement Frequency [Axis] Measurement Frequency [Axis] Derivative assets — current Derivative Assets, Current [Member] Line item in the statement of financial position in a classified presentation in which the fair value amounts of the derivative instruments are included. Net cash provided by (used in) operating activities Net Cash Provided by (Used in) Operating Activities Notes payable Short-term Debt Fair Value, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Entity Tax Identification Number Entity Tax Identification Number Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Basic (in shares) Weighted average shares - basic (in shares) Weighted Average Number of Shares Outstanding, Basic Earnings per share, Diluted (usd per share) Earnings Per Share, Diluted Segment [Domain] Segments [Domain] Deferred financing cost amortization Amortization of Debt Issuance Costs and Discounts Service cost Defined Benefit Plan, Service Cost Long-term Contract for Purchase of Electric Power [Axis] Long-term Contract for Purchase of Electric Power [Axis] Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net Hedging Relationship [Axis] Hedging Relationship [Axis] Income taxes Income Taxes Paid, Net Interest Expense Interest Expense [Member] Subsequent Events Subsequent Events [Text Block] Other regulatory assets Other Regulatory Assets [Member] Other regulatory assets [Member] Intangible assets, net Intangible Assets, Net (Excluding Goodwill) Comprehensive income available for common stock Comprehensive Income (Loss), Net of Tax, Attributable to Parent Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent [Member] Regulatory Liability [Domain] Regulatory Liability [Domain] Net cash provided by financing activities Net Cash Provided by (Used in) Financing Activities Treasury stock, at cost – 43,885 and 32,492 shares, respectively Treasury Stock, Value Other comprehensive income (loss), net of tax: Other Comprehensive Income (Loss), Net of Tax [Abstract] Deferred income tax liabilities, net Deferred Income Tax Liabilities, Net Credit Risk Derivative Liabilities, at Fair Value Collateral Already Posted, Aggregate Fair Value Natural gas in storage Energy Related Inventory, Natural Gas in Storage Accounts payable Accounts Payable, Current Condensed Statement of Income Captions [Line Items] Condensed Statement of Income Captions [Line Items] Depreciation, depletion and amortization Depreciation, Depletion and Amortization Energy [Axis] Energy [Axis] Effective Income Tax Reconciliation, Tax Benefit From Amortization Of Excess Deferred Income Taxes Effective Income Tax Reconciliation, Tax Benefit From Amortization Of Excess Deferred Income Taxes Effective Income Tax Reconciliation, Tax Benefit From Amortization Of Excess Deferred Income Taxes Schedule of Fair Value Hierarchy, Measured on Recurring Basis Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Environmental Environmental [Member] Environmental costs associated with utility property [Member] Accumulated Other Comprehensive Income (loss) AOCI Attributable to Parent [Member] Materials, supplies and fuel Increase (Decrease) in Inventories Beginning balance (in shares) Ending balance (in shares) Common Stock, Shares, Outstanding Colorado Public Utilities Commission (CPUC) Colorado Public Utilities Commission (CPUC) [Member] Colorado Public Utilities Commission (CPUC) [Member] Derivative [Table] Derivative [Table] Long Long [Member] Materials and supplies Inventory, Raw Materials and Supplies, Gross Regulatory Asset [Domain] Regulatory Asset [Domain] Estimated Future Employer Contributions in Current Fiscal Year Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year Unusual or Infrequent Item, or Both [Domain] Unusual or Infrequent Item, or Both [Domain] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Nebraska Gas Black Hills Energy, Nebraska Gas [Member] Black Hills Energy, Nebraska Gas Schedule Of Regulatory Assets And Liabilities [Table] Schedule Of Regulatory Assets And Liabilities [Table] A table of assets and liabilities that are created when regulatory agencies permit public utilities to defer recognitiion of certain revenues or costs included in rate setting. Income Statement Location [Domain] Income Statement Location [Domain] Debt Instrument, Term Debt Instrument, Term Market - off-system sales Market Off-System Sales [Member] Market Off-System Sales [Member] Colorado Electric Black Hills Energy, Colorado Electric [Member] Black Hills Energy, Colorado Electric Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Fuel Type [Domain] Fuel Type [Domain] Fuel Type [Domain] Total property, plant and equipment, net Property, Plant and Equipment, Net Total operating expenses Operating Expenses Other deferred credits and other liabilities Other Liabilities, Noncurrent Long-term debt - repayments Repayments of Long-term Debt Earnings per share of common stock: Earnings Per Share [Abstract] Derivative Assets, Commodity Derivatives Derivative Asset Property, plant and equipment Property, Plant and Equipment, Gross Document Quarterly Report Document Quarterly Report Revenues Total revenues Revenues Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax Line of Credit Facility [Table] Line of Credit Facility [Table] Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Long-term debt, net of current maturities Long-term Debt, Excluding Current Maturities Unusual or Infrequent Item, or Both [Axis] Unusual or Infrequent Item, or Both [Axis] Accounts payable and other current liabilities Increase (Decrease) in Other Accounts Payable and Accrued Liabilities Regulatory Assets and Liabilities Disclosure [Abstract] Regulatory Assets and Liabilities Disclosure [Abstract] Document Fiscal Period Focus Document Fiscal Period Focus Effective Tax Rate Effective Income Tax Rate Reconciliation, Percent (Tax) benefit on benefit plan liability adjustments - prior service costs Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Tax Reclassification out of Accumulated Other Comprehensive Income [Domain] Reclassification out of Accumulated Other Comprehensive Income [Domain] Net income Net income Net income (loss) Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Accounts receivable, trade Accounts Receivable, before Allowance for Credit Loss, Current Estimated Future Employer Contributions in Next Fiscal Year Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year Derivative, Nonmonetary Notional Amount Derivative, Nonmonetary Notional Amount Unrecorded Unconditional Purchase Obligation [Line Items] Unrecorded Unconditional Purchase Obligation [Line Items] Regulatory assets, non-current Regulatory Assets, Noncurrent Cash, restricted cash and cash equivalents at beginning of period Cash, restricted cash and cash equivalents at end of period Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Fuel Type [Axis] Fuel Type [Axis] Generation Fuel Source, Wind, Coal, Solar Consolidation, Eliminations Consolidation, Eliminations [Member] Common stock, par value (usd per share) Common Stock, Par or Stated Value Per Share Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan Disclosure [Line Items] Current assets: Assets, Current [Abstract] Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] Other financing activities Proceeds from (Payments for) Other Financing Activities Settlement Total of Plan to Provide TCJA and State Tax Reform benefits to Customers Settlement Total of Plan to Provide TCJA and State Tax Reform benefits to Customers Settlement Total of Plan to Provide TCJA and State Tax Reform benefits to Customers Entity Central Index Key Entity Central Index Key Security Exchange Name Security Exchange Name Natural gas options purchased, net Commodity Option [Member] Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] Diluted (in shares) Weighted average shares - diluted (in shares) Weighted Average Number of Shares Outstanding, Diluted Other comprehensive income, net of tax Other comprehensive income, net of tax Other Comprehensive Income (Loss), Net of Tax Fair Value, Measurements, Recurring Fair Value, Recurring [Member] Accrued interest Interest Payable, Current Income Taxes Income Tax Disclosure [Text Block] Cost of removal Removal Costs [Member] Current Fiscal Year End Date Current Fiscal Year End Date Services transferred at a point in time Transferred at Point in Time [Member] Write-offs and Other Deductions Accounts Receivable, Allowance for Credit Loss, Writeoff Schedule of Net Benefit Costs Schedule of Net Benefit Costs [Table Text Block] Measurement Basis [Axis] Measurement Basis [Axis] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block] Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Other income (expense): Nonoperating Income (Expense) [Abstract] Regulatory liabilities Increase (Decrease) in Regulatory Liabilities Public Utilities Amount of System Safety and Integrity Rider Moved to Base Rates Requested Public Utilities Amount of System Safety and Integrity Rider Moved to Base Rates Requested Public Utilities Amount of System Safety and Integrity Rider Moved to Base Rates Requested Not Designated as Hedging Instrument Not Designated as Hedging Instrument [Member] Credit Facility [Axis] Credit Facility [Axis] Net cash (used in) investing activities Net Cash Provided by (Used in) Investing Activities Portion at Fair Value Measurement Portion at Fair Value Measurement [Member] Changes in certain operating assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Less: accumulated depreciation and depletion Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Operating activities: Net Cash Provided by (Used in) Operating Activities [Abstract] Fair Value Hedge Assets Fair Value Hedge Assets Schedule of Short-term Debt Schedule of Short-term Debt [Table Text Block] Total current liabilities Liabilities, Current Inter-company Revenues Intersegment Eliminations [Member] (Tax) benefit on reclassification of net realized (gains) losses on settled/amortized derivatives Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, Tax Public Utilities General Disclosures [Table] Public Utilities General Disclosures [Table] Line of Credit Facility, Maximum Borrowing Capacity Line of Credit Facility, Maximum Borrowing Capacity Reclassification out of Accumulated Other Comprehensive Income Reclassification out of Accumulated Other Comprehensive Income [Member] Term loan - borrowings Proceeds from Other Short-term Debt Segment Reporting Information Segment Reporting Information [Line Items] Entity Address, Postal Zip Code Entity Address, Postal Zip Code Position [Domain] Position [Domain] Intercompany Customers Intercompany Customers [Member] Intercompany Customers [Member] External Customers External Customers [Member] External Customers Taxes - property and production Taxes, Miscellaneous Transportation Transportation [Member] Transportation [Member] Line of Credit Facility [Line Items] Line of Credit Facility [Line Items] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Title of 12(b) Security Title of 12(b) Security Regulatory liabilities, current Less current regulatory liabilities Regulatory Liability, Current Other current assets Other Assets, Current Statement [Table] Statement [Table] Global Settlement agreement with KCC Staff and various intervenors for a general rate increase and renewal of its safety and integrity rider. Global Settlement agreement with KCC Staff and various intervenors for a general rate increase and renewal of its safety and integrity rider. [Member] Global Settlement agreement with KCC Staff and various intervenors for a general rate increase and renewal of its safety and integrity rider. Recently Issued and Adopted Accounting Standards New Accounting Pronouncements, Policy [Policy Text Block] Dilutive effect of: Dilutive Securities, Effect on Basic Earnings Per Share [Abstract] Public Utilities, Number of Days After Filing a Rate Review the Interim Rates May Be Implemented Public Utilities, Number of Days After Filing a Rate Review the Interim Rates May Be Implemented Public Utilities, Number of Days After Filing a Rate Review the Interim Rates May Be Implemented Public Utilities, Requested Rate Increase (Decrease), Amount Public Utilities, Requested Rate Increase (Decrease), Amount Regulatory liabilities Regulatory Assets and Liabilities, Other Disclosures [Abstract] Statistical Measurement [Axis] Statistical Measurement [Axis] Derivative Liability, Fair Value, Gross Liability Derivative Liability, Fair Value, Gross Liability Derivative, Remaining Maturity Derivative, Remaining Maturity Subsequent Event Subsequent Event [Member] Cover [Abstract] Goodwill Goodwill Fuel, purchased power and cost of natural gas sold Cost of Sales [Member] (Tax) benefit on reclassification adjustment of benefit plan liability - net loss Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, Tax Natural gas basis swaps purchased Basis Swap [Member] Solar Solar [Member] Electric Generation Source - Solar Adjustments to reconcile net income to net cash provided by (used in) operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Defined Benefit Pension Plans Pension Plan [Member] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Public Utilities, Requested Debt Capital Structure, Percentage Public Utilities, Requested Debt Capital Structure, Percentage Loss on reacquired debt Loss on Reacquired Debt [Member] Unrealized Gain (Loss) on Price Risk Cash Flow Derivatives, before Tax Unrealized Gain (Loss) on Price Risk Cash Flow Derivatives, before Tax Schedule of Derivative Instruments in Statement of Financial Position, Fair Value Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block] Accumulated Defined Benefit Plans Adjustment Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] Netting Contract Category [Axis] Netting Contract Category [Axis] Netting Contract Category Deferred income taxes Deferred Income Tax Expense (Benefit)