Organization, Consolidation and Presentation of Financial Statements [Abstract] Schedule of Error Corrections and Prior Period Adjustment Restatement [Table] Schedule of Error Corrections and Prior Period Adjustment Restatement [Table] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Cash and Cash Equivalents Cash and Cash Equivalents [Member] Accounts Payable Accounts Payable [Member] Scenario [Axis] Scenario [Axis] Scenario, Unspecified [Domain] Scenario, Unspecified [Domain] Restatement Adjustment Restatement Adjustment [Member] Error Corrections and Prior Period Adjustments Restatement [Line Items] Error Corrections and Prior Period Adjustments Restatement [Line Items] Prior period reclassification adjustment Prior Period Reclassification Adjustment Net cash provided by (used in) operating activities Net Cash Provided by (Used in) Operating Activities Debt Disclosure [Abstract] Schedule of Short-term Debt [Table] Schedule of Short-term Debt [Table] Credit Facility [Axis] Credit Facility [Axis] Credit Facility [Domain] Credit Facility [Domain] Revolving Credit Facility Revolving Credit Facility [Member] CP Program Commercial Paper [Member] Variable Rate [Axis] Variable Rate [Axis] Variable Rate [Domain] Variable Rate [Domain] Base Rate Base Rate [Member] Eurodollar Eurodollar [Member] Letter of Credit Letter of Credit [Member] Short-term Debt [Line Items] Short-term Debt [Line Items] Notes payable Short-term Debt Letters of Credit Letters of Credit Outstanding, Amount Line of Credit Facility, Current Borrowing Capacity Line of Credit Facility, Current Borrowing Capacity Number Of One-Year Extension Options Number Of One-Year Extension Options Number Of One-Year Extension Options; related to a revolving credit facility. Debt Instrument, Term Debt Instrument, Term Line of Credit Facility, Maximum Borrowing Capacity Line of Credit Facility, Maximum Borrowing Capacity Line of Credit Facility, Interest Rate at Period End Line of Credit Facility, Interest Rate at Period End Line of Credit Facility, Unused Capacity, Commitment Fee Percentage Line of Credit Facility, Unused Capacity, Commitment Fee Percentage Commercial Paper, Maximum Borrowing Capacity Commercial Paper, Maximum Borrowing Capacity Commercial Paper, Maximum Borrowing Capacity Short-term Debt, Weighted Average Interest Rate Short-term Debt, Weighted Average Interest Rate Income Statement [Abstract] Revenue Revenue, Net Operating expenses: Operating Expenses [Abstract] 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. 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. Depreciation, depletion and amortization Depreciation, Depletion and Amortization Taxes - property, production and severance Taxes, Miscellaneous Impairment of long-lived assets Impairment of Long-Lived Assets Held-for-use Other operating expenses Other Cost and Expense, Operating Total operating expenses Operating Expenses Operating income Operating Income (Loss) Other income (expense): Nonoperating Income (Expense) [Abstract] Interest charges - Interest and Debt Expense [Abstract] Interest expense incurred (including amortization of debt issuance costs, premiums and discounts) Interest Costs Incurred Allowance for funds used during construction - borrowed Public Utilities Allowance For Funds Used During Construction Borrowed Interest Costs Capitalized The component of the allowance for funds used during construction during the period which represents the approximate composite costs of borrowed funds and is netted against interest expense. Capitalized interest Interest Costs Capitalized Adjustment Interest income Investment Income, Interest Allowance for funds used during construction - equity Public Utilities, Allowance for Funds Used During Construction, Capitalized Cost of Equity Other income (expense), net Other Nonoperating Income (Expense) Total other income (expense), net Nonoperating Income (Expense) Income before income taxes Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest Income tax benefit (expense) Income Tax Expense (Benefit) Net income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Net income attributable to noncontrolling interest Net Income (Loss) Attributable to Noncontrolling Interest Net income available for common stock Net Income (Loss) Available to Common Stockholders, Basic Earnings per share of common stock: Earnings Per Share [Abstract] Earnings (loss) per share, Basic (usd per share) Earnings Per Share, Basic Earnings (loss) per share, Diluted (usd per share) Earnings Per Share, Diluted Basic (in shares) Weighted Average Number of Shares Outstanding, Basic Diluted (in shares) Weighted Average Number of Shares Outstanding, Diluted Dividends declared per share of common stock (usd per share) Common Stock, Dividends, Per Share, Declared Derivative Instruments and Hedging Activities Disclosure [Abstract] Risk Management Activities Derivative Instruments and Hedging Activities Disclosure [Text Block] Statement of Cash Flows [Abstract] Operating activities: Net Cash Provided by (Used in) Operating Activities [Abstract] Net income (loss) Net income available for common stock Adjustments to reconcile net income to net cash provided by operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Deferred financing cost amortization Amortization of Debt Issuance Costs and Discounts Impairment of long-lived assets Impairment of Oil and Gas Properties Derivative fair value adjustments Unrealized Gain (Loss) on Derivatives and Commodity Contracts Stock compensation Share-based Compensation Deferred income taxes Deferred Income Tax Expense (Benefit) Employee benefit plans Pension and Other Postretirement Benefit Expense Other adjustments, net Other Noncash Income (Expense) Changes in certain operating assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Materials, supplies and fuel Increase (Decrease) in Inventories Accounts receivable, unbilled revenues and other operating assets Increase (Decrease) in Accounts Receivable and Other Operating Assets Accounts payable and other operating liabilities Increase (Decrease) in Other Accounts Payable and Accrued Liabilities Regulatory assets - current Increase (Decrease) in Other Regulatory Assets Regulatory liabilities - current Increase (Decrease) in Regulatory Liabilities Contributions to defined benefit pension plans Pension Contributions Interest rate swap settlement Gain (Loss) on Sale of Derivatives Other operating activities, net Increase (Decrease) in Other Operating Assets and Liabilities, Net Net cash provided by (used in) operating activities Investing activities: Net Cash Provided by (Used in) Investing Activities [Abstract] Property, plant and equipment additions Payments to Acquire Property, Plant, and Equipment Acquisition, net of long term debt assumed Business Combination, Consideration Transferred, Net of Long Term Debt and Cash Acquired Business Combination, Consideration Transferred, Net of Long Term Debt and Cash Acquired Other investing activities Payments for (Proceeds from) Other Investing Activities Net cash provided by (used in) investing activities Net Cash Provided by (Used in) Investing Activities Financing activities: Net Cash Provided by (Used in) Financing Activities [Abstract] Dividends paid on common stock Payments of Dividends Common stock issued Proceeds from Issuance of Common Stock Sale of noncontrolling interest Proceeds from Noncontrolling Interests Net (payments) borrowings of short-term debt Proceeds from (Repayments of) Short-term Debt Long-term debt - issuances Proceeds from Issuance of Long-term Debt Long-term debt - repayments Repayments of Long-term Debt Distributions to noncontrolling interest Payments to Noncontrolling Interests Other financing activities Proceeds from (Payments for) Other Financing Activities Net cash provided by (used in) financing activities Net Cash Provided by (Used in) Financing Activities Net change in cash and cash equivalents Cash and Cash Equivalents, Period Increase (Decrease) Cash and cash equivalents, beginning of period Cash and Cash Equivalents, at Carrying Value Cash and cash equivalents, end of period Segment Reporting Information, Additional Information [Abstract] Segment Reporting Schedule of Segment Reporting Information, by Segment [Table Text Block] Reconciliation of Assets from Segment to Consolidated Reconciliation of Assets from Segment to Consolidated [Table Text Block] Statement of Comprehensive Income [Abstract] Other Comprehensive Income (Loss) Comprehensive Income (Loss) Note [Text Block] Business Segment Information Segment Reporting Disclosure [Text Block] Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] Accumulated Defined Benefit Plans Adjustment Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] AOCI Attributable to Parent AOCI Attributable to Parent [Member] Derivative Instrument [Axis] Derivative Instrument [Axis] Derivative Contract [Domain] Derivative Contract [Domain] Interest Rate Swaps Interest Rate Swap [Member] Commodity Contract Commodity Contract [Member] Reclassification Out Of Accumulated Other Comprehensive Income [Axis] Reclassification out of Accumulated Other Comprehensive Income [Axis] Reclassification Out Of Accumulated Other Comprehensive Income [Domain] Reclassification out of Accumulated Other Comprehensive Income [Domain] Reclassification Out Of Accumulated Other Comprehensive Income Reclassification out of Accumulated Other Comprehensive Income [Member] Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] AOCI Attributable to Parent, Net of Tax [Roll Forward] Accumulated Other Comprehensive Income [Roll Forward] Accumulated Other Comprehensive Income [Roll Forward] Accumulated Other Comprehensive Income (Loss), Net of Tax, Period Start Accumulated Other Comprehensive Income (Loss), Net of Tax Other Comprehensive Income (Loss), before Reclassifications, Net of Tax Other Comprehensive Income (Loss), before Reclassifications, Net of Tax Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax Accumulated Other Comprehensive Income (Loss), Net of Tax, Period End Receivables [Abstract] Schedule of Accounts, Notes, Loans and Financing Receivable [Table] Schedule of Accounts, Notes, Loans and Financing Receivable [Table] Segments [Axis] Segments [Axis] Segment [Domain] Segments [Domain] Electric Utilities Electric Utilities [Member] Electric Utilities Segment [Member] Gas Utilities Gas Utilities [Member] Gas Utilities [Member] Power Generation Power Generation [Member] Power Generation Mining Mining [Member] Mining Oil and Gas Oil and Gas [Member] Oil and Gas [Member] Consolidation Items [Axis] Consolidation Items [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Corporate Corporate, Non-Segment [Member] Accounts Receivable [Line Items] Accounts, Notes, Loans and Financing Receivable [Line Items] Accounts Receivable, Trade Accounts Receivable, Gross, Current Unbilled Receivables, Current Unbilled Receivables, Current Allowance for Doubtful Accounts Allowance for Doubtful Accounts Receivable, Current Accounts receivable, net Accounts Receivable, Net, Current Fair Value Disclosures [Abstract] Fair Value of Financial Instruments Fair Value Disclosures [Text Block] Derivative [Table] Derivative [Table] Energy [Axis] Energy [Axis] Energy [Domain] Energy [Domain] Natural Gas, Distribution Natural Gas, Distribution [Member] Natural Gas for distribution [Member] Future Future [Member] Commodity Option Commodity Option [Member] Basis Swap Basis Swap [Member] Fixed for Float Swaps Purchased Fixed for Float Swaps Purchased [Member] Fixed for Float Swaps Purchased [Member] Natural Gas Physical Purchases Natural Gas Physical Purchases [Member] Natural Gas Physical Purchases [Member] Hedging Relationship [Axis] Hedging Relationship [Axis] Hedging Relationship [Domain] Hedging Relationship [Domain] Cash Flow Hedging Cash Flow Hedging [Member] Derivative [Line Items] Derivative [Line Items] Derivative, Nonmonetary Notional Amount Derivative, Nonmonetary Notional Amount Maximum Term (in months) Derivative, Remaining Maturity Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months Schedule of Derivative Instruments Schedule of Derivative Instruments [Table Text Block] Contract or Notional Amounts and Terms of Commodity Derivatives Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block] Derivative Instruments, Gain (Loss) Derivative Instruments, Gain (Loss) [Table Text Block] Statement of Stockholders' Equity [Abstract] Schedule of Stockholders Equity Schedule of Stockholders Equity [Table Text Block] Schedule of Variable Interest Entities Schedule of Variable Interest Entities [Table Text Block] Accounts Receivable Loans, Notes, Trade and Other Receivables Disclosure [Text Block] Asset Impairment Charges [Abstract] Impairment of Assets Asset Impairment Charges [Text Block] Reconciliation of Assets from Segment to Consolidated [Table] Reconciliation of Assets from Segment to Consolidated [Table] Segment Reporting, Asset Reconciling Item [Line Items] Segment Reporting, Asset Reconciling Item [Line Items] Assets Assets Derivative Instruments, Gain (Loss) [Table] Derivative Instruments, Gain (Loss) [Table] Interest rate swaps Income Statement Location [Axis] Income Statement Location [Axis] Income Statement Location [Domain] Income Statement Location [Domain] Interest expense Interest Expense [Member] Revenue Sales Revenue, Net [Member] Fuel, purchased power and cost of natural gas sold Cost of Sales [Member] Hedging Designation [Axis] Hedging Designation [Axis] Hedging Designation [Domain] Hedging Designation [Domain] Designated as Hedging Instrument Designated as Hedging Instrument [Member] Derivative Instruments, Gain (Loss) [Line Items] Derivative Instruments, Gain (Loss) [Line Items] Amount of Reclassified Gain/(Loss) from AOCI into Income (Effective Portion) Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net Amount of Gain/(Loss) Recognized in Income on Derivative (Ineffective Portion) Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net Derivative, Gain (Loss) on Derivative, Net Derivative, Gain (Loss) on Derivative, Net Statement [Table] Statement [Table] Parent Parent [Member] Noncontrolling Interest Noncontrolling Interest [Member] Statement [Line Items] Statement [Line Items] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Total Equity, beginning balance Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Net income (loss) Net Income (Loss) Including Portion Attributable to Noncontrolling Interest (Excluding Income Loss Attributable to Redeemable Noncontrolling Interest) Net Income (Loss) Including Portion Attributable to Noncontrolling Interest (Excluding Income Loss Attributable to Redeemable Noncontrolling Interest) Other comprehensive income (loss) Other Comprehensive Income (Loss), Net of Tax Dividends on common stock Dividends, Common Stock, Cash Share-based compensation Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures Issuance of common stock Stock Issued During Period, Value, New Issues Dividend reinvestment and stock purchase plan Stock Issued During Period, Value, Dividend Reinvestment Plan Redeemable noncontrolling interest Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests Cumulative effect of ASU 2016-09 implementation Adjustment to Additional Paid in Capital, Income Tax Effect from Share-based Compensation, Net Other stock transactions Stockholders' Equity, Other Distribution to noncontrolling interest Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Sale of noncontrolling interest Noncontrolling Interest, Increase from Sale of Parent Equity Interest Total Equity, ending balance Regulatory Assets and Liabilities Disclosure [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] Common Stock Common Stock [Member] 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 Offering Program Shares Issued At The Market Equity Offering Program Shares Issued At The Market Equity Offering Program Shares Issued 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 Payments of Stock Issuance Costs Payments of Stock Issuance Costs Fair Value of Financial Instruments Fair Value, by Balance Sheet Grouping [Table Text Block] Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Corporate Term Loan Due August 2019 Corporate Term Loan Due August 2019 [Member] Corporate Term Loan Due August 2019 [Member] Debt Instrument [Line Items] Debt Instrument [Line Items] Extinguishment of Debt, Amount Extinguishment of Debt, Amount Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract] Schedule of Net Benefit Costs Schedule of Net Benefit Costs [Table Text Block] 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] Line of Credit Facility [Table] Line of Credit Facility [Table] Range [Axis] Range [Axis] Range [Domain] Range [Domain] Maximum Maximum [Member] Line of Credit Facility [Line Items] Line of Credit Facility [Line Items] 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 Debt Instrument, Consolidated Indebtedness To Capitalization Ratio Requirement For The Next Fiscal Year Recourse Leverage Ratio Recourse Leverage Ratio Recourse Leverage Ratio Debt instrument, covenant, Leverage Recourse Ratio Debt Instrument, Covenant, Recourse Leverage Ratio The maximum allowed recourse leverage ratio under debt covenants. Schedule of Short-term Debt Schedule of Short-term Debt [Table Text Block] Schedule of Credit Facility Covenants Credit Facility and Short Term Debt Covenants [Table Text Block] Schedule of significant debt covenants related to Credit Facility and other short-term debt [Table Text Block] Not Designated as Hedging Instrument Not Designated as Hedging Instrument [Member] Regulatory Asset [Axis] Regulatory Asset [Axis] Regulatory Asset [Domain] Regulatory Asset [Domain] Gas price derivatives Price Risk Derivative [Member] Regulatory Assets Regulatory Assets Management's Statement Organization, Consolidation, Basis of Presentation, Business Description and Accounting Policies [Text Block] Business Combinations [Abstract] Business Combination, Pro Forma Information Business Acquisition, Pro Forma Information [Table Text Block] Income Tax Disclosure [Abstract] Income Taxes Income Tax Disclosure [Text Block] Payables and Accruals [Abstract] Schedule of Accrued Liabilities Schedule of Accrued Liabilities [Table Text Block] Accrued Liabilities Accounts Payable and Accrued Liabilities Disclosure [Text Block] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] Black Hills Corporation Black Hills Corporation [Member] Black Hills Corporation [Member] Senior Unsecured Notes Due 2027 Senior Unsecured Notes Due 2027 [Member] Senior Unsecured Notes Due 2027 [Member] Notional Amount Derivative, Notional Amount Derivative, Loss on Derivative Derivative, Loss on Derivative Long-term Debt, Gross Long-term Debt, Gross Derivative Instruments, Loss Recognized in Other Comprehensive Income (Loss), Effective Portion Derivative Instruments, Loss Recognized in Other Comprehensive Income (Loss), Effective Portion Derivative Instruments, Income Statement Location of Gain (Loss) Reclassified from Accumulated OCI Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net Derivative, Average Fixed Interest Rate Derivative, Average Fixed Interest Rate Derivative liabilities, current Derivative Liability, Current Derivative Expired During the Period Derivative Expired During the Period Derivative Expired During the Period Regulatory Accounting Schedule of Regulatory Assets and Liabilities [Text Block] Acquisition Business Combination Disclosure [Text Block] Schedule of Impaired Long-Lived Assets Held and Used [Table] Schedule of Impaired Long-Lived Assets Held and Used [Table] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Domain] Property, Plant and Equipment, Type [Domain] Assets Not Expected To Be Utilized In Cost Of Service Gas Program Assets Not Expected To Be Utilized In Cost Of Service Gas Program [Member] Assets Not Expected To Be Utilized In Cost Of Service Gas Program [Member] Impairment of Oil and Gas Properties Average Natural Gas Price Per MCF, NYMEX Average Natural Gas Price Per MCF, NYMEX Average Natural Gas Price Per MCF, NYMEX. The average price is calculated using the price at the first day of each month for each of the preceding 12 months. Average Natural Gas Price Per MCF, Wellhead Average Natural Gas Price Per MCF, Wellhead Average Natural Gas Price Per MCF, Wellhead. The average price is calculated using the price at the first day of each month for each of the preceding 12 months. Average Crude Oil Price, Per Barrel, NYMEX Average Crude Oil Price, Per Barrel, NYMEX Average Crude Oil Price, Per Barrel, NYMEX. Average price is calculated using the price at the first day of each month for each of the preceding 12 months. Average Crude Oil Price Per Barrel, Wellhead Average Crude Oil Price Per Barrel, Wellhead Average Crude Oil Price Per Barrel, Wellhead. The average price is calculated using the price at the first day of each month for each of the preceding 12 months. Results of Operations, Impairment of Oil and Gas Properties Results of Operations, Impairment of Oil and Gas Properties Variable Interest Entity, Primary Beneficiary Variable Interest Entity, Primary Beneficiary [Member] Electric Generation Capacity, Megawatts Electric Generation Capacity, Megawatts Electric Generation Capacity, Megawatts Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage Current assets Assets, Current Property, plant and equipment of variable interest entities, net Property, Plant and Equipment, Gross Current liabilities Liabilities, Current Accrued employee compensation, benefits and withholdings Employee-related Liabilities, Current Accrued property taxes Accrual for Taxes Other than Income Taxes, Current Customer deposits and prepayments Customer Advances and Deposits, Current Accrued interest and contract adjustment payments Interest Payable, Current CIAC current portion Customer Advances for Construction Other (none of which is individually significant) Other Accrued Liabilities, Current Total accrued liabilities Accrued Liabilities, Current Crude Oil Futures Crude Oil Options Options Held [Member] Natural Gas Futures and Swaps Swap [Member] Crude Oil Crude Oil [Member] Natural Gas Natural Gas [Member] Equity Stockholders' Equity Note Disclosure [Text Block] Fair Value Measurements Derivatives and Fair Value [Text Block] Inventory, Net [Abstract] Materials, Supplies and Fuel Inventory Disclosure [Text Block] Weighted average shares - basic (in shares) Dilutive effect of: Dilutive Securities, Effect on Basic Earnings Per Share [Abstract] Equity Units (in shares) Incremental Common Shares Attributable to Dilutive Effect of Equity Unit Purchase Agreements Equity compensation (in shares) Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements Weighted average shares - diluted (in shares) Segment Reporting Segment Reporting, Policy [Policy Text Block] Use of Estimates and Basis of Presentation Use of Estimates, Policy [Policy Text Block] Revisions Reclassification, Policy [Policy Text Block] Recently Issued and Adopted Accounting Standards New Accounting Pronouncements, Policy [Policy Text Block] Earnings Per Share Earnings Per Share [Text Block] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] 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. Derivative Assets, Non-current Derivative Assets, 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. 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. Derivative Liabilities, Non-current 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. Derivatives, Carrying Amount and Fair Value [Line Items] Derivatives, Fair Value [Line Items] Derivative Asset, Fair Value, Gross Asset Derivative Asset, Fair Value, Gross Asset Derivative Asset, Fair Value, Gross Liability Derivative Asset, Fair Value, Gross Liability Derivative Liability, Fair Value, Gross Asset Derivative Liability, Fair Value, Gross Asset Derivative Liability, Fair Value, Gross Liability Derivative Liability, Fair Value, Gross Liability Derivative Asset, Fair Value, Net Derivative Asset, Fair Value, Amount Not Offset Against Collateral Derivative Liability, Fair Value, Net Derivative Liability, Fair Value, Amount Not Offset Against Collateral Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Business Acquisition [Axis] Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] Source Gas Source Gas [Member] Source Gas [Member] Business Acquisition [Line Items] Business Acquisition [Line Items] Acquisition Narrative [Abstract] Acquisition Narrative [Abstract] Acquisition Narrative [Abstract] Business Combination, Consideration Transferred, Net of Long Term Debt and Cash Acquired Long-term debt assumed Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt Business Combination, Acquisition Related Costs Business Combination, Acquisition Related Costs Business Acquisition, Pro Forma Information [Abstract] Business Acquisition, Pro Forma Information [Abstract] Pro Forma - Revenue Business Acquisition, Pro Forma Revenue Pro Forma - Net income (loss) available for common stock Business Acquisition, Pro Forma Net Income (Loss) Pro Forma - Earnings per share, Basic (usd per share) Business Acquisition, Pro Forma Earnings Per Share, Basic Pro Forma - Earnings per share, Diluted (usd per share) Business Acquisition, Pro Forma Earnings Per Share, Diluted Accounts Receivable and Allowance for Doubtful Accounts Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block] Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners Payments for Repurchase of Redeemable Noncontrolling Interest Payments for Repurchase of Redeemable Noncontrolling Interest Notes Payable and Long-term Debt Debt Disclosure [Text Block] Other comprehensive income (loss), net of tax: Other Comprehensive Income (Loss), Net of Tax [Abstract] Reclassification adjustments of benefit plan liability - prior service cost Other Comprehensive (Income) Loss, Amortization Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Prior Service Cost (Credit), Net of Tax Reclassification adjustments of benefit plan liability - net gain (loss) Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Gain (Loss), Net of Tax Net unrealized gains (losses) Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax Reclassification of net realized (gains) losses Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax Other comprehensive income (loss), net of tax Comprehensive income Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Less: comprehensive income attributable to noncontrolling interest Net Income (Loss) Attributable to Redeemable Noncontrolling Interest Comprehensive income available for common stock Comprehensive Income (Loss), Net of Tax, Attributable to Parent Document and Entity Information [Abstract] Abstract model section heading for document and entity information Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Document Type Document Type Document Period End Date Document Period End Date Amendment Flag Amendment Flag Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Current Fiscal Year End Date Current Fiscal Year End Date Entity Current Reporting Status Entity Current Reporting Status Entity Filer Category Entity Filer Category Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Entity Well-known Seasoned Issuer Entity Well-known Seasoned Issuer Entity Voluntary Filers Entity Voluntary Filers Effective Income Tax Rate Reconciliation, Percent [Abstract] Effective Income Tax Rate Reconciliation, Percent [Abstract] Federal statutory rate Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent State income tax (net of federal tax effect) Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent Percentage depletion in excess of cost Effective Income Tax Rate Reconciliation, Nondeductible Expense, Depletion, Percent Accounting for uncertain tax positions adjustment Effective Income Tax Rate Reconciliation, Tax Contingency, Percent Noncontrolling interest Effective Income Tax Rate Reconciliation, Noncontrolling Interest Income (Loss), Percent IRC 172(f) carryback claim Effective Income Tax Rate Reconciliation, NOL Carryback Specified Liability Loss Effective Income Tax Rate Reconciliation, NOL Carryback Specified Liability Loss Tax credits Effective Income Tax Rate Reconciliation, Tax Credit, Percent Effective tax rate adjustment Effective Income Tax Rate Reconciliation, Inter-period Tax Allocation, Percent Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to an inter-period tax allocation. Flow-through adjustments Effective Income Tax Rate Reconciliation, Flow Through Accounting The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate that can be explained by Flow Through Accounting. Transaction costs Effective Income Tax Rate Reconciliation, Nondeductible Expense, Restructuring Charges, Percent Effective Income Tax Rate Reconciliation Allowance For Other Funds Used During Construction, Equity Effective Income Tax Rate Reconciliation Allowance For Other Funds Used During Construction, Equity The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate that can be explained by the equity portion of allowance for other funds used during construction, a nondeductible expense. Other tax differences Effective Income Tax Rate Reconciliation, Other Adjustments, Percent Effective Tax Rate Effective Income Tax Rate Reconciliation, Percent IRS Settlement [Abstract] IRS Settlement [Abstract] IRS Settlement [Abstract] Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities Income Tax Examination, Increase (Decrease) In Accrued Interest Income Tax Examination, Increase (Decrease) In Accrued Interest Income Tax Examination, Increase (Decrease) In Accrued Interest. The amount the liability recorded for interest expense on income tax examination increased (decreased) in the current year / accounting period. Income Tax Examination, Liability (Refund) Adjustment from Settlement with Taxing Authority Income Tax Examination, Liability (Refund) Adjustment from Settlement with Taxing Authority Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Measurement Basis [Axis] Measurement Basis [Axis] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Portion at Fair Value Measurement Portion at Fair Value Measurement [Member] Carrying Amount Reported Value Measurement [Member] Fair Value Estimate of Fair Value Measurement [Member] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Cash and cash equivalents Cash and cash equivalents, Fair Value Cash and Cash Equivalents, Fair Value Disclosure Restricted cash and equivalents Restricted Cash and Investments, Current Restricted Cash Fair Value Disclosure Restricted Cash Fair Value Disclosure This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This element represents the fair value of assets categorized as restricted cash Notes payable, Fair Value Short-term Debt, Fair Value Long-term debt, including current maturities Long-term Debt Long-term debt, including current maturities, Fair Value Long-term Debt, Fair Value Subsequent Events [Abstract] Schedule of Subsequent Events Schedule of Subsequent Events [Table Text Block] Supplemental Cash Flow Information [Abstract] Non-cash Investing and Financing Activities from Continuing Operations [Abstract] Noncash Investing and Financing Items [Abstract] Property, plant and equipment acquired with accrued liabilities Capital Expenditures Incurred but Not yet Paid Increase (decrease) in capitalized assets associated with asset retirement obligations Increase (Decrease) in Asset Retirement Obligations Supplemental Cash Flow Elements [Abstract] Supplemental Cash Flow Elements [Abstract] Interest (net of amounts capitalized) Interest Paid, Net Income taxes, net Income Taxes Paid, Net Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost (Credit) Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent [Member] Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member] Interest Rate Contract Interest Rate Contract [Member] Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items] Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] Interest expense Income (loss) before earnings (loss) of unconsolidated subsidiaries and income taxes Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Materials, Supplies and Fuel Schedule of Inventory, Current [Table Text Block] Supplemental Disclosure of Cash Flow Information Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Subsequent Event [Table] Subsequent Event [Table] Disposal Group Classification [Axis] Disposal Group Classification [Axis] Disposal Group Classification [Domain] Disposal Group Classification [Domain] Discontinued Operations, Held-for-sale Discontinued Operations, Held-for-sale [Member] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Subsequent Event Subsequent Event [Member] Subsequent Event [Line Items] Subsequent Event [Line Items] Divestiture of Oil and Gas Business Subsequent Event, Description Schedule of Fair Value Hierarchy, Measured on Recurring Basis Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Schedule of Derivative Instruments Balance Sheet Location Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block] Reclassification adjustment of benefit plan - prior service cost, (tax) benefit Other Comprehensive (Income) Loss, Amortization Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Prior Service Cost (Credit), Tax Reclassification adjustment of benefit plan liabilities, (tax) benefit Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, Tax Net unrealized gains/losses, (tax) benefit Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax Reclassification of net realized gains/losses, (tax) benefit Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Inter-company eliminations Intersegment Eliminations [Member] Consolidation, Eliminations Consolidation, Eliminations [Member] Business Combination, Separately Recognized Transactions [Axis] Business Combination, Separately Recognized Transactions [Axis] Business Combination, Separately Recognized Transactions [Domain] Business Combination, Separately Recognized Transactions [Domain] Incremental, Non-Recurring Acquisition Costs (Net of Tax) Incremental, Non-Recurring Acquisition Costs (Net of Tax) [Member] Net of Tax [Member] Labor (Net Of Tax) Labor (Net Of Tax) [Member] Labor (Net Of Tax) [Member] Segment Reporting Information Segment Reporting Information [Line Items] Net Income (Loss) Attributable to Redeemable Noncontrolling Interest Tax benefit recognized from Carryback claims for specified liability losses involving prior tax years Operating Loss Carryback Operating Loss Carryback - Carryback claims for specified liabiliy losses involving prior tax years Net tax benefit Tax Adjustments, Settlements, and Unusual Provisions Impairment of Oil and Gas Properties Net of Tax Impairment Of Oil And Gas Properties, Net Of Tax Impairment Of Oil And Gas Properties, Net Of Tax Schedule of Effective Income Tax Rate Reconciliation Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Schedule of Related Party Transactions, by Related Party [Table] Schedule of Related Party Transactions, by Related Party [Table] Business Group [Axis] Business Group [Axis] Business Group (grouping of segments) [Axis] Business Group [Domain] Business Group [Domain] [Domain] for Business Group (grouping of segments) [Axis] Utilities Group Utilities Group [Member] Utilities Group - consists of our Electric Utilities and our Gas Utilities segments Related Party Transaction [Line Items] Related Party Transaction [Line Items] Restricted Net Assets for Subsidiaries Restricted Net Assets for Subsidiaries Amount of Restricted Net Assets (Equity) for Subsidiaries as of the end of the reporting period. Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] Measurement Frequency [Axis] Measurement Frequency [Axis] Fair Value, Measurement Frequency [Domain] Fair Value, Measurement Frequency [Domain] Fair Value, Measurements, Recurring Fair Value, Measurements, Recurring [Member] Fair Value, Hierarchy [Axis] Fair Value, Hierarchy [Axis] Fair Value Hierarchy [Domain] Fair Value Hierarchy [Domain] Fair Value, Inputs, Level 1 Fair Value, Inputs, Level 1 [Member] Fair Value, Inputs, Level 2 Fair Value, Inputs, Level 2 [Member] Fair Value, Inputs, Level 3 Fair Value, Inputs, Level 3 [Member] Estimate of Fair Value Measurement 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] Derivative Assets, Commodity Derivatives Derivative Asset Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset Derivative Assets, Total Assets, Fair Value Disclosure Derivative Liabilities, Fair Value Disclosure Derivative Liability Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset Derivative Liabilities, Total Financial and Nonfinancial Liabilities, Fair Value Disclosure Employee Benefit Plans Pension and Other Postretirement Benefits Disclosure [Text Block] Schedule of Earnings Per Share Reconciliation Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] 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] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Antidilutive Securities [Axis] Antidilutive Securities [Axis] Antidilutive Securities, Name [Domain] Antidilutive Securities, Name [Domain] Equity compensation Stock Compensation Plan [Member] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Anti-dilutive shares Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Statement of Financial Position [Abstract] ASSETS Assets [Abstract] Current assets: Assets, Current [Abstract] Accounts receivable, net Materials, supplies and fuel Inventory, Net Derivative assets, current Derivative Asset, Current Regulatory assets, current Regulatory Assets, Current Other current assets Other Assets, Current Total current assets Investments Long-term Investments Property, plant and equipment Less: accumulated depreciation and depletion Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Total property, plant and equipment, net Property, Plant and Equipment, Net Other assets: Other Assets, Noncurrent [Abstract] Goodwill Goodwill Intangible assets, net Intangible Assets, Net (Excluding Goodwill) Regulatory assets, non-current Regulatory Assets, Noncurrent Derivative assets, non-current Derivative Asset, Noncurrent Other assets, non-current Other Assets, Noncurrent Total other assets, non-current Assets, Noncurrent, Other than Noncurrent Investments and Property, Plant and Equipment TOTAL ASSETS LIABILITIES, REDEEMABLE NONCONTROLLING INTEREST AND TOTAL EQUITY Liabilities and Equity [Abstract] Current liabilities: Liabilities, Current [Abstract] Accounts payable Accounts Payable, Current Accrued liabilities Accrued income taxes, net Accrued Income Taxes Regulatory liabilities, current Regulatory Liability, Current Current maturities of long-term debt Long-term Debt, Current Maturities Total current liabilities Long-term debt Long-term Debt, Excluding Current Maturities Deferred credits and other liabilities: Liabilities, Noncurrent [Abstract] Deferred income tax liabilities, net, non-current Deferred Tax Liabilities, Net, Noncurrent Derivative liabilities, non-current Derivative Liability, Noncurrent Regulatory liabilities, non-current Regulatory Liability, Noncurrent Benefit plan liabilities Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent Other deferred credits and other liabilities Other Liabilities, Noncurrent Total deferred credits and other liabilities Liabilities, Noncurrent Commitments and contingencies (See Notes 8, 10, 15, 16) Commitments and Contingencies Redeemable noncontrolling interest Redeemable Noncontrolling Interest, Equity, Other, Carrying Amount Equity: Stockholders' Equity Attributable to Parent [Abstract] Common stock $1 par value; 100,000,000 shares authorized; issued 53,524,529; 53,397,467; and 53,131,469 shares, respectively Common Stock, Value, Issued Additional paid-in capital Additional Paid in Capital Retained earnings Retained Earnings (Accumulated Deficit) Treasury stock, at cost – 41,457; 15,258; and 22,368 shares, respectively Treasury Stock, Value Accumulated other comprehensive income (loss) Total stockholders’ equity Stockholders' Equity Attributable to Parent Noncontrolling interest Noncontrolling Interest in Variable Interest Entity Total equity TOTAL LIABILITIES, REDEEMABLE NONCONTROLLING INTEREST AND TOTAL EQUITY Liabilities and Equity Reclassification Out of Accumulated Other Comprehensive Income (Loss) Reclassification out of Accumulated Other Comprehensive Income [Table Text Block] Schedule of Accumulated Other Comprehensive Income (Loss) Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Subsequent Events Subsequent Events [Text Block] Schedule of Retained Earnings Adjustments [Table] Schedule of Retained Earnings Adjustments [Table] Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] Adjustments for New Accounting Pronouncement Accounting Standards Update 2016-09 [Member] Accounting Standards Update 2016-09 Compensation - Stock Compensation (Topic 718): Improvments to employee Share-Based Payment Accounting Retained Earnings Adjustments [Line Items] Retained Earnings Adjustments [Line Items] Cumulative-effect adjustment to retained earnings Cumulative Effect on Retained Earnings, Net of Tax Schedule of Defined Benefit Plans Disclosures [Table] Schedule of Defined Benefit Plans Disclosures [Table] Defined Benefit Plans and Other Postretirement Benefit Plans [Axis] Defined Benefit Plans and Other Postretirement Benefit Plans [Axis] Defined Benefit Plan and Other Postretirement Benefit Plan [Domain] Defined Benefit Plan and Other Postretirement Benefit Plan [Domain] Defined Benefit Pension Plans Pension Plan [Member] Defined Benefit Postretirement Healthcare Plans Other Postretirement Benefit Plan [Member] Supplemental Non-qualified Defined Benefit and Defined Contribution Plans Supplemental Employee Retirement Plan [Member] Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan Disclosure [Line Items] Defined Benefit Plan, Net Periodic Benefit Cost [Abstract] Defined Benefit Plan, Net Periodic Benefit Cost [Abstract] Service cost Defined Benefit Plan, Service Cost Interest cost Defined Benefit Plan, Interest Cost Expected return on plan assets Defined Benefit Plan, Expected Return on Plan Assets Prior service cost (benefit) Defined Benefit Plan, Amortization of Prior Service Cost (Credit) Net loss (gain) Defined Benefit Plan, Amortization of Gains (Losses) Net periodic benefit cost Defined Benefit Plan, Net Periodic Benefit Cost Pension and Other Postretirement Benefit Contributions [Abstract] Pension and Other Postretirement Benefit Contributions [Abstract] Contributions by Employer Defined Benefit Plan, Contributions by Employer Estimated Future Employer Contributions in Current Fiscal Year Defined Benefit Plans, Estimated Future Employer Contributions in Current Fiscal Year Estimated Future Employer Contributions in Next Fiscal Year Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year 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. Deferred energy and fuel cost adjustments - current Deferred Fuel Costs [Member] Deferred gas cost adjustments Asset Recoverable Gas Costs [Member] 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. Employee benefit plans Pension and Other Postretirement Plans Costs [Member] Environmental Environmental [Member] Environmental costs associated with utility property [Member] Asset retirement obligations Asset Retirement Obligation Costs [Member] Loss on reacquired debt Loss on Reacquired Debt [Member] Renewable energy standard adjustment Renewable Energy Program [Member] Flow through accounting Flow Through Accounting [Member] The income tax effects of certain tax items are reflected in cost of service for the customer in which the tax benefits are realized and result in lower utiity rates. 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] Decommissioning costs Environmental Restoration Costs [Member] Gas supply contract termination Gas Supply Contract Termination [Member] Gas Supply Contract Termination [Member] Other regulatory assets Other Regulatory Assets [Member] Other regulatory assets [Member] Regulatory Liability [Axis] Regulatory Liability [Axis] Regulatory Liability [Domain] Regulatory Liability [Domain] Deferred energy and gas costs Cost of removal Removal Costs [Member] Revenue subject to refund Revenue Subject to Refund [Member] Other regulatory liabilities Other Regulatory Liabilities [Member] Other regulatory liabilities [Member] Regulatory Agency [Axis] Regulatory Agency [Axis] Regulatory Agency [Domain] Regulatory Agency [Domain] South Dakota Public Utilities Commission (SDPUC) South Dakota Public Utilities Commission (SDPUC) [Member] South Dakota Public Utilities Commission (SDPUC) [Member] Catastrophic Event [Axis] Catastrophic Event [Axis] Catastrophic Event [Domain] Catastrophic Event [Domain] Winter Storm Atlas Catastrophe [Member] Scenario, Previously Reported Scenario, Previously Reported [Member] Schedule Of Regulatory Assets And Liabilities [Line Items] Schedule Of Regulatory Assets And Liabilities [Line Items] Schedule of regulatory asset and liabilities line items Regulatory Asset, Amortization Period Regulatory Asset, Amortization Period Regulatory Liability, Amortization Period Regulatory Liability, Amortization Period Regulatory Liabilities Regulatory Liabilities Approximate increase in annual amortization expense due to change in amortization periods Amortization of Regulatory Asset Materials and supplies Inventory, Raw Materials and Supplies, Gross Fuel - Electric Utilities Energy Related Inventory, Other Fossil Fuel Natural gas in storage held for distribution Energy Related Inventory, Natural Gas in Storage Total materials, supplies and fuel Common Stock, Par Value (usd per share) Common Stock, Par or Stated Value Per Share Common Stock, Shares Issued Common Stock, Shares, Issued Treasury Stock, Shares Treasury Stock, Shares Common Stock, Shares Authorized Common Stock, Shares Authorized Supplemental Disclosure of Cash Flow Information Cash Flow, Supplemental Disclosures [Text Block]