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Asset Class [Domain] Asset Class [Domain] Sale of Stock, Price Per Share Sale of Stock, Price Per Share Entity File Number Entity File Number Deferred energy and fuel cost adjustments Deferred energy and gas costs Deferred Fuel Costs [Member] Contributions by Employer Defined Benefit Plan, Plan Assets, Contributions by Employer Impairment of investment Impairment of investment Other Asset Impairment Charges Benefit plan liability adjustments - net gain (loss) (tax) benefit Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, Tax 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] Equity Stockholders' Equity Note Disclosure [Text Block] Interest expense incurred net of amounts capitalized (including amortization of debt issuance costs, premiums and discounts) Interest Expense [Member] Use of Estimates and Basis of Presentation Use of Estimates, Policy [Policy Text Block] Local Phone Number Local Phone Number Public Utilities, Regulatory Proceeding [Domain] Public Utilities, Regulatory Proceeding [Domain] 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 Net (payments) borrowings of short-term debt Proceeds from (Repayments of) Short-term Debt Accounts receivable, net Accounts receivable, net Accounts Receivable, after Allowance for Credit Loss, Current Decommissioning costs Environmental Restoration Costs [Member] Other investments Investments [Member] Additional paid-in capital Additional Paid in Capital Total other income (expense) Nonoperating Income (Expense) Management's Statement Organization, Consolidation, Basis of Presentation, Business Description and Accounting Policies [Text Block] Investment in privately held oil and gas company Equity Securities [Member] Reconciliation of Assets from Segment to Consolidated [Table] Reconciliation of Assets from Segment to Consolidated [Table] Reclassification of net realized gains/losses, (tax) benefit Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Regulatory Agency [Axis] Regulatory Agency [Axis] Letters of Credit Letters of Credit Outstanding, Amount Total current assets Assets, Current Entity Current Reporting Status Entity Current Reporting Status Other Nonoperating Income (Expense) Including Allowance For Funds Used During Construction, Equity Other Nonoperating Income (Expense) Including Allowance For Funds Used During Construction, Equity Other Nonoperating Income (Expense) Including Allowance For Funds Used During Construction, Equity Natural gas physical contracts, net Natural Gas Physical Purchases [Member] Natural Gas Physical Purchases [Member] Deferred credits and other liabilities: Liabilities, Noncurrent [Abstract] Net income available for common stock Net income available for common stock Net Income (Loss) Attributable to Parent Common Stock Common Stock [Member] Current assets: Assets, Current [Abstract] Schedule of Short-term Debt [Table] Schedule of Short-term Debt [Table] Debt Instrument [Axis] Debt Instrument [Axis] Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Deferred financing cost amortization Amortization of Debt Issuance Costs and Discounts Derivative, Gain (Loss) on Derivative, Net Derivative, Gain (Loss) on Derivative, Net Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair Value Measurements Derivatives and Fair Value [Text Block] Net income Net income Net income (loss) Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Product and Service [Axis] Product and Service [Axis] Supplemental Non-qualified Defined Benefit and Defined Contribution Plans Supplemental Employee Retirement Plan [Member] AOCI Attributable to Parent, Net of Tax [Roll Forward] Accumulated Other Comprehensive Income [Roll Forward] Accumulated Other Comprehensive Income [Roll Forward] Entity Small Business Entity Small Business Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] Scenario [Axis] Scenario [Axis] Black Hills Wyoming and Wyoming Electric Black Hills Wyoming and Wyoming Electric [Member] Black Hills Wyoming and Wyoming Electric [Member] Document and Entity Information [Abstract] Document and Entity Information [Abstract] Abstract model section heading for document and entity information Entity Filer Category Entity Filer Category Net unrealized gains/losses on commodity derivatives, (tax) benefit Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax Electricity Electricity [Member] Other (none of which is individually significant) Other Accrued Liabilities, Current Fuel - Electric Utilities Energy Related Inventory, Other Fossil Fuel Corporate Corporate, Non-Segment [Member] Other deferred credits and other liabilities Derivative Liabilities, Noncurrent [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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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 Commodity Contract Commodity Contract [Member] Net income attributable to noncontrolling interest Net Income (Loss) Attributable to Noncontrolling Interest Net Income (Loss) Attributable to Noncontrolling Interest Rate Review Filed with the Regulatory Agency Rate Review Filed with the Regulatory Agency [Member] Rate Review Filed with the Regulatory Agency [Member] Line of Credit Facility [Table] Line of Credit Facility [Table] Reclassification out of Accumulated Other Comprehensive Income Reclassification out of Accumulated Other Comprehensive Income [Member] Retained Earnings Retained Earnings [Member] Services transferred over time Transferred over Time [Member] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Public Utilities, General Disclosures [Line Items] Public Utilities, General Disclosures [Line Items] Total deferred credits and other liabilities Liabilities, Other than Long-term Debt, Noncurrent Accrued property, plant and equipment purchases at June 30 Capital Expenditures Incurred but Not yet Paid Document Period End Date Document Period End Date Other current assets Other Assets, Current Statement [Table] Statement [Table] Entity Registrant Name Entity Registrant Name Dividends paid on common stock Payments of Dividends Schedule of Defined Benefit Plans Contributions Schedule of Defined Benefit Plans Contributions [Table Text Block] Schedule of Defined Benefit Plans Contributions for the current year and specific future years.[Text Block] Schedule of Fair Value Hierarchy, Measured on Recurring Basis Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Cumulative Effect, Period of Adoption [Domain] Cumulative Effect, Period of Adoption [Domain] Cumulative Effect, Period of Adoption Investing activities: Net Cash Provided by (Used in) Investing Activities [Abstract] Maximum Maximum [Member] Service cost Defined Benefit Plan, Service Cost Electric wholesale contracts Energy Related Derivative [Member] Designated as Hedging Instrument Designated as Hedging Instrument [Member] Unbilled revenue Unbilled Receivables, Current Net income available for common stock Net Income (Loss) Available to Common Stockholders, Basic Derivatives, Fair Value [Line Items] Derivatives, Fair Value [Line Items] Reclassification adjustments of benefit plan liability - prior service cost (net of tax of $6, $5, $13 and $10, respectively) Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, after Tax Gas Utilities Gas Utilities [Member] Gas Utilities [Member] Antidilutive Securities, Name [Domain] Antidilutive Securities, Name [Domain] Account Receivable Schedule Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block] Retained earnings Retained Earnings (Accumulated Deficit) Entity Tax Identification Number Entity Tax Identification Number Senior Unsecured Notes Due 2030 Senior Unsecured Notes Due 2030 [Member] Senior Unsecured Notes Due 2030 Regulatory liabilities - current Increase (Decrease) in Regulatory Liabilities Revenue Recognition Revenue [Policy Text Block] Earnings (loss) per share, Diluted (usd per share) Earnings Per Share, Diluted Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Schedule of Net Benefit Costs Schedule of Net Benefit Costs [Table Text Block] Electric Utilities Electric Utilities [Member] Electric Utilities Segment [Member] Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, Tax Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, Tax Power Generation Power Generation [Member] Power Generation Trading Symbol Trading Symbol At The Market Equity Offering Program Authorized Aggregate Value At The Market Equity Offering Program Authorized Aggregate Value At The Market Equity Offering Program authorized an aggregate value that the Company may, through its sales agents, offer and sell from time to time shares of its common stock. 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 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. 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Pension Accounting Asset Method Pension and Other Postretirement Plans, Policy [Policy Text Block] Public Utilities, Regulatory Proceeding [Axis] Public Utilities, Regulatory Proceeding [Axis] Interest expense incurred net of amounts capitalized (including amortization of debt issuance costs, premiums and discounts) Interest Expense Interest Costs Incurred Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Schedule of Accounts, Notes, Loans and Financing Receivable [Table] Schedule of Accounts, Notes, Loans and Financing Receivable [Table] Schedule of Accumulated Other Comprehensive Income (Loss) Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Proceeds from Issuance of Debt Proceeds from Issuance of Debt Retail - Electric , Natural Gas and Coal Retail - Electric , Natural Gas and Coal [Member] Retail - Electric , Natural Gas and Coal Operating activities: Net Cash Provided by (Used in) Operating Activities [Abstract] Total operating expenses Operating Expenses Operating Expenses Dilutive effect of: Dilutive Securities, Effect on Basic Earnings Per Share [Abstract] Unrecorded Unconditional Purchase Obligation, Term Unrecorded Unconditional Purchase Obligation, Term Other regulatory liabilities Other Regulatory Liabilities [Member] Other regulatory liabilities [Member] Other income (expense): Nonoperating Income (Expense) [Abstract] Reclassification of net realized (gains) losses Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax Black Hills Energy, Colorado Gas Black Hills Energy, Colorado Gas [Member] Black Hills Energy, Colorado Gas [Member] Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan Disclosure [Line Items] Segment Reporting Schedule of Segment Reporting Information, by Segment [Table Text Block] Natural gas in storage Energy Related Inventory, Natural Gas in Storage Measurement Basis [Axis] Measurement Basis [Axis] At The Market Equity Offering Program Shares Issued At The Market Equity Offering Program Shares Issued At The Market Equity Offering Program Shares Issued Derivative, Remaining Maturity Derivative, Remaining Maturity Public Utilities, Approved Return on Equity, Percentage Public Utilities, Approved Return on Equity, Percentage Customer [Domain] Customer [Domain] Debt Disclosure [Abstract] Debt Disclosure [Abstract] Materials, Supplies, and Fuel Schedule Schedule of Inventory, Current [Table Text Block] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Derivative Instrument [Axis] Derivative Instrument [Axis] Income Statement Location [Domain] Income Statement Location [Domain] Statistical Measurement [Axis] Statistical Measurement [Axis] Supplemental Cash Flow Information [Abstract] Supplemental Cash Flow Information [Abstract] Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] Pending FERC Approval - Number of Megawatts Capacity to be Purchased and Delivered Through Intercompany Agreement FERC Approved - Number of Megawatts Capacity to be Purchased and Delivered Through Intercompany Agreement FERC Approved - Number of Megawatts Capacity to be Purchased and Delivered Through Intercompany Agreement Other Comprehensive Income (Loss) Comprehensive Income (Loss) Note [Text Block] Condensed Statement of Comprehensive Income [Table] Condensed Statement of Comprehensive Income [Table] Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Income taxes Income Taxes Paid, Net 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] Timing of Transfer of Good or Service [Domain] Timing of Transfer of Good or Service [Domain] Customer deposits and prepayments Customer Deposits and Prepayments Accrued Liabilities - Customer Deposits and Prepayments Unrecorded Unconditional Purchase Obligation [Line Items] Unrecorded Unconditional Purchase Obligation [Line Items] Investments Investment [Text Block] Notes Payable, Current Maturities and Debt Debt Disclosure [Text Block] Accounts Receivable, Allowance for Credit Loss, Writeoff Accounts Receivable, Allowance for Credit Loss, Writeoff Long-term Debt, Term Long-term Debt, Term Regulatory Matters Schedule of Regulatory Assets and Liabilities [Text Block] Reclassification out of Accumulated Other Comprehensive Income [Domain] Reclassification out of Accumulated Other Comprehensive Income [Domain] Common Stock Authorized (in shares) Common Stock, Shares Authorized Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Total other assets, non-current Assets, Noncurrent, Other than Noncurrent Investments and Property, Plant and Equipment Long-term Contract for Purchase of Electric Power [Domain] Long-term Contract for Purchase of Electric Power [Domain] Entity Central Index Key Entity Central Index Key Entity Emerging Growth Company Entity Emerging Growth Company Noncontrolling Interest Noncontrolling Interest [Member] Sale of Stock [Domain] Sale of Stock [Domain] Stock compensation Share-based Payment Arrangement, Noncash Expense Schedule of Earnings Per Share Reconciliation Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Other operating activities, net Increase (Decrease) in Other Operating Assets and Liabilities, Net Risk Management and Derivatives Derivative Instruments and Hedging Activities Disclosure [Text Block] Distributions to noncontrolling interest Payments to Noncontrolling Interests Long-term debt, net of current maturities Long-term Debt, Excluding Current Maturities Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months Derivative [Table] Derivative [Table] Payments of Stock Issuance Costs Payments of Stock Issuance Costs Credit Facility [Domain] Credit Facility [Domain] Loss on reacquired debt Loss on Reacquired Debt [Member] Accrued employee compensation, benefits and withholdings Employee-related Liabilities, Current Fair Value, Inputs, Level 2 Fair Value, Inputs, Level 2 [Member] Income Taxes Income Tax Disclosure [Text Block] Employee benefit plans Pension and Other Postretirement Benefits Cost (Reversal of Cost) Antidilutive Securities [Axis] Antidilutive Securities [Axis] Number of Megawatts Capacity Purchased Number of Megawatts Capacity Purchased Number of Megawatts Capacity Purchased Nebraska Publc Service Commission (NPSC) Nebraska Publc Service Commission (NPSC) [Member] Nebraska Publc Service Commission (NPSC) Public Utilities, Requested Rate Increase (Decrease), Amount Public Utilities, Requested Rate Increase (Decrease), Amount Regulatory liabilities Regulatory Assets and Liabilities, Other Disclosures [Abstract] LIABILITIES AND EQUITY Liabilities and Equity [Abstract] 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. Reconciliation of Assets from Segment to Consolidated Reconciliation of Assets from Segment to Consolidated [Table Text Block] Share-based compensation, shares Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture Other assets, non-current Other Assets, Noncurrent Financing activities: Net Cash Provided by (Used in) Financing Activities [Abstract] Other comprehensive income, net of tax Other comprehensive income (loss), net of tax Other Comprehensive Income (Loss), Net of Tax Derivative Contract [Domain] Derivative Contract [Domain] Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization, Consolidation and Presentation of Financial Statements [Abstract] Long-term Debt Long-term Debt Derivative assets, current Derivative Asset, Current Segment Reporting Segment Reporting, Policy [Policy Text Block] Public Utilities, Requested Equity Capital Structure, Percentage Public Utilities, Requested Equity Capital Structure, Percentage Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Property, plant and equipment additions Payments to Acquire Property, Plant, and Equipment Reclassification Out of Accumulated Other Comprehensive Income (Loss) Reclassification out of Accumulated Other Comprehensive Income [Table Text Block] Long-term debt - issuances Proceeds from Issuance of Long-term Debt Accrued interest Interest Payable, Current Other regulatory assets Other Regulatory Assets [Member] Other regulatory assets [Member] Income tax receivable, net Income Taxes Receivable, Current Accounts receivable and other current assets Increase (Decrease) in Accounts Receivable and Other Operating Assets Retirement Plan Type [Domain] Retirement Plan Type [Domain] Public Utilities, Requested Debt Capital Structure, Percentage Public Utilities, Requested Debt Capital Structure, Percentage 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] Accounts Receivable, Allowance for Credit Loss, Recovery Accounts Receivable, Allowance for Credit Loss, Recovery Net unrealized gains (losses) on commodity derivatives (net of tax of $14, $119, $68 and $65, respectively) Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax Regulatory liabilities, non-current Regulatory Liability, Noncurrent Sale of Stock [Axis] Sale of Stock [Axis] Accounts Receivable, Credit Loss Expense (Reversal) Accounts Receivable, Credit Loss Expense (Reversal) Valuation Approach and Technique [Axis] Valuation Approach and Technique [Axis] Derivative Assets, Commodity Derivatives Derivative Asset Additional Paid-in Capital Additional Paid-in Capital [Member] Revenue Revenue from Contract with Customer [Text Block] Ratio of Indebtedness to Net Capital Ratio of Indebtedness to Net Capital Interest income Investment Income, Interest Bonds Due 2024 Bonds Due 2024 [Member] Bonds Due 2024 [Member] Receivable [Domain] Receivable [Domain] Payment for Pension Benefits Payment for Pension Benefits Deferred income tax liabilities, net Deferred Income Tax Liabilities, Net City of Colorado Springs City of Colorado Springs [Member] City of Colorado Springs Common Stock, Dividends, Per Share, Cash Paid Common Stock, Dividends, Per Share, Cash Paid Fair Value Measurement [Domain] Fair Value Measurement [Domain] Environmental Environmental [Member] Environmental costs associated with utility property [Member] Schedule of Short-term Debt Schedule of Short-term Debt [Table Text Block] Debt Instrument, Interest Rate, Stated Percentage Debt Instrument, Interest Rate, Stated Percentage Valuation Approach and Technique [Domain] Valuation Approach and Technique [Domain] Colorado Public Utilities Commission (CPUC) Colorado Public Utilities Commission (CPUC) [Member] Colorado Public Utilities Commission (CPUC) [Member] Restricted cash and equivalents Restricted Cash and Investments, Current Entity Address, Address Line One Entity Address, Address Line One Property, plant and equipment Property, Plant and Equipment, Gross Entity Address, State or Province Entity Address, State or Province Income Statement Location [Axis] Income Statement Location [Axis] Black Hills Energy, Nebraska Gas Black Hills Energy, Nebraska Gas [Member] Black Hills Energy, Nebraska Gas Derivative Liabilities, Total Financial and Nonfinancial Liabilities, Fair Value Disclosure Retirement Benefits [Abstract] Retirement Benefits [Abstract] Inter-company Revenues Intersegment Eliminations [Member] Net cash (used in) investing activities Net Cash Provided by (Used in) Investing Activities Fair Value, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] 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. Derivative, Nonmonetary Notional Amount Derivative, Nonmonetary Notional Amount Market - off-system sales Market Off-System Sales [Member] Market Off-System Sales [Member] Contract or notional amounts and terms of marketing activities and derivative commodity instruments Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block] Investments, All Other Investments [Abstract] Investments, All Other Investments [Abstract] Benefit plan liabilities Liability, Defined Benefit Plan, Noncurrent Accounts payable Accounts Payable, Current Other Comprehensive Income (Loss), before Reclassifications, Net of Tax Other Comprehensive Income (Loss), before Reclassifications, Net of Tax Taxes - property and production Taxes, Miscellaneous Accrued liabilities Total accrued liabilities Accrued Liabilities, Current Entity Interactive Data Current Entity Interactive Data Current Common Stock Issued (in shares) Common Stock, Shares, Issued Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Common Stock, Par Value (usd per share) Common Stock, Par or Stated Value Per Share Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Materials, supplies and fuel Total materials, supplies and fuel Inventory, Net Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Regulatory assets - current Increase (Decrease) in Other Regulatory Assets Prior service cost (benefit) Defined Benefit Plan, Amortization of Prior Service Cost (Credit) Pension Plan Defined Benefit Pension Plans Pension Plan [Member] Measurement Frequency [Axis] Measurement Frequency [Axis] Earnings Per Share Earnings Per Share [Text Block] Less: accumulated depreciation and depletion Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Revolving Credit Facility Revolving Credit Facility [Member] Issuance of common stock, shares Stock Issued During Period, Shares, New Issues Hedging Designation [Axis] Hedging Designation [Axis] Cost of Sales Cost of Sales [Member] Effective Tax Rate Effective Income Tax Rate Reconciliation, Percent Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Long-term Debt, Fair Value Long-term Debt, Fair Value 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] Extinguishment of Debt, Amount Extinguishment of Debt, Amount Reclassification Reclassification, Policy [Policy Text Block] Common stock $1 par value; 100,000,000 shares authorized; issued 62,772,996 and 61,480,658 shares, respectively Common Stock, Value, Issued Line of Credit Facility [Line Items] Line of Credit Facility [Line Items] Net loss (gain) Defined Benefit Plan, Amortization of Gain (Loss) Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] Materials, supplies and fuel Increase (Decrease) in Inventories Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Equity compensation (in shares) Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements Basic (in shares) Weighted average shares - basic (in shares) Weighted Average Number of Shares Outstanding, Basic Public Utilities, Number of Gas Distribution Territories Consolidating Public Utilities, Number of Gas Distribution Territories Consolidating Public Utilities, Number of Gas Distribution Territories Consolidating Equity Components [Axis] Equity Components [Axis] 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] Total stockholders’ equity Stockholders' Equity Attributable to Parent Regulatory assets Net Regulatory Assets [Abstract] Materials and supplies Inventory, Raw Materials and Supplies, Gross Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset Depreciation, depletion and amortization Depreciation, Depletion and Amortization Scenario, Adjustment Scenario, Adjustment [Member] Inter-company Operating Revenue Intercompany Customers [Member] Intercompany Customers [Member] External Operating Revenue External Customers [Member] External Customers Accounts receivable, trade Accounts Receivable, before Allowance for Credit Loss, Current Transportation Transportation [Member] Transportation [Member] Interest (net of amounts capitalized) Interest Paid, Excluding Capitalized Interest, Operating Activities Other Postretirement Benefits Plan Other Postretirement Benefits Plan [Member] Energy [Domain] Energy [Domain] Security Exchange Name Security Exchange Name Anti-dilutive shares (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Regulatory assets, non-current Regulatory Assets, Noncurrent Regulatory assets Regulatory assets Regulatory Assets Comprehensive income Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Reclassification out of Accumulated Other Comprehensive Income [Axis] Reclassification out of Accumulated Other Comprehensive Income [Axis] Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities Discount Rate Used in Valuation of Fair Value of Oil and Gas Reserve Quantities Discount Rate Used in Valuation of Fair Value of Oil and Gas Reserve Quantities Discount Rate Used in Valuation of Fair Value of Oil and Gas Reserve Quantities Payment for Pension and Other Postretirement Benefits [Abstract] Payment for Pension and Other Postretirement Benefits [Abstract] Equity Component [Domain] Equity Component [Domain] Hedging Relationship [Domain] Hedging Relationship [Domain] Gas price derivatives Price Risk Derivative [Member] Document Transition Report Document Transition Report Interest expense, net Interest Income (Expense), Net Reclassification adjustments of benefit plan liability - net gain (net of tax of $(182), $(52), $(277) and $(105), respectively) Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, after Tax Cash Flow Hedging Cash Flow Hedging [Member] Cumulative Effect, Period of Adoption Adjustment Cumulative Effect, Period of Adoption Adjustment [Member] Cumulative Effect, Period of Adoption Adjustment Cumulative Effect, Period of Adoption [Axis] Cumulative Effect, Period of Adoption [Axis] Cumulative Effect, Period of Adoption Regulatory assets, current Less current regulatory assets Regulatory Assets, Current Hedging Relationship [Axis] Hedging Relationship [Axis] Deferred gas cost adjustments Asset Recoverable Gas Costs [Member] Not Designated as Hedging Instrument Not Designated as Hedging Instrument [Member] Income Statement [Abstract] Income Statement [Abstract] South Dakota Electric South Dakota Electric [Member] South Dakota Electric [Member] Fair Value Hedge Liabilities Fair Value Hedge Liabilities Balance Sheet Location [Axis] Balance Sheet Location [Axis]