Document And Entity Information us-gaap_DerivativeNotionalAmount Derivative, Notional Amount Note To Financial Statement Details Textual us-gaap_DerivativeGainLossOnDerivativeNet Change in fair value of derivative Significant Accounting Policies Note 4 - Other Long-term Assets Note 5 - Bank Debt Note 6 - Accounts Payable and Accrued Liabilities Distribution from investment in Sunrise Energy Note 8 - Other Operating Income Bank debt, net (Note 5) Note 10 - Stock Compensation Plans Not Designated as Hedging Instrument [Member] Note 11 - Leases Long-term liabilities: Note 13 - Net Income (Loss) Per Share Note 14 - Fair Value Measurements Income Tax Disclosure [Text Block] Note 4 - Other Long-term Assets - Other Long-term Assets (Details) Note 5 - Bank Debt - Bank Debt, Less Debt Issuance Costs (Details) Hedging Designation [Axis] Note 5 - Bank Debt - Maximum Leverage Ratio (Details) Hedging Designation [Domain] Note 6 - Accounts Payable and Accrued Liabilities - Accounts Payable and Accrued Liabilities (Details) Note 8 - Other Operating Income - Other Operating Income (Details) us-gaap_LiabilitiesCurrent Total current liabilities Note 10 - Stock Compensation Plans - RSU Activity (Details) Schedule of Debt [Table Text Block] Note 10 - Stock Compensation Plans - RSU Activity (Details) (Parentheticals) Note 10 - Stock Compensation Plans - Vesting of Non-vested RSU Grants (Details) Note 11 - Leases - Information Related to Leases (Details) Note 11 - Leases - Future Minimum Lease Payments (Details) Note 13 - Net Income (Loss) Per Share - Computation of Net Income(Loss) Allocated to Common Shareholders (Details) Note 14 - Fair Value Measurements - Financial Assets and Liabilities Measured on a Recurring Basis at Fair Value (Details) Note 14 - Fair Value Measurements - Change in Fair Value of the Fuel Hedges and Interest Rate Swaps (Details) Notes To Financial Statements Notes To Financial Statements [Abstract] us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueOutstanding Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Outstanding us-gaap_DerivativeVariableInterestRate Derivative, Variable Interest Rate Share price on grant date (in dollars per share) us-gaap_DerivativeNumberOfInstrumentsHeld Derivative, Number of Instruments Held, Total Share price on vesting date (in dollars per share) Proceeds from sale of marketable securities Fair value of interest rate swaps Share-based Payment Arrangement, Restricted Stock Unit, Activity [Table Text Block] us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod Forfeited (in shares) us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber Non-vested grants at December 31, 2019 (in shares) Non-vested grants at June 30, 2020 (in shares) Proceeds from maturities of certificates of deposit Granted – share price on grant date was $0.98 (in shares) us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod Vested – average weighted share price on vesting date was $0.68 (in shares) us-gaap_LongTermDebtCurrent Net current portion Current portion of PPP note (Note 5) us-gaap_UnderlyingDerivativeVolume Underlying, Derivative Volume (in USD per Gallon) Current portion of bank debt, net (Note 5) us-gaap_DerivativeNonmonetaryNotionalAmountVolume Derivative, Nonmonetary Notional Amount, Volume (Gallon) Accounts payable and accrued liabilities (Note 6) us-gaap_ContractWithCustomerLiabilityCurrent Contract with Customer, Liability, Current Lessee, Operating Leases [Text Block] Revolving Credit Facility [Member] Capital expenditures included in accounts payable and prepaid expense Credit Facility [Axis] Credit Facility [Domain] us-gaap_PolicyTextBlockAbstract Accounting Policies Proceeds from sale of equipment Proceeds from sale of royalty interests in oil properties us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in shares) us-gaap_PaymentsToAcquirePropertyPlantAndEquipment Capital expenditures Current liabilities: WEIGHTED AVERAGE SHARES OUTSTANDING Vesting [Axis] Vesting [Domain] Asset Impairment Charges [Text Block] SUPPLEMENTAL CASH FLOW INFORMATION: us-gaap_Assets Total Assets Disclosure of Share-based Compensation Arrangements by Share-based Payment Award [Table Text Block] Property, plant and equipment, at cost: Other Assets Disclosure [Text Block] us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic Net income (loss) allocated to common shareholders Share-based Payment Arrangement [Text Block] us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation Taxes paid on vesting of RSUs Award Type [Domain] Restricted cash (Note 12) Restricted Cash and Cash Equivalents, Total Restricted cash Award Type [Axis] Net income (loss) NET INCOME (LOSS) Restricted Stock Units (RSUs) [Member] Coal [Member] London Interbank Offered Rate (LIBOR) Swap Rate [Member] us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment Less - accumulated DD&A us-gaap_PropertyPlantAndEquipmentNet Total property, plant and equipment, net us-gaap_PropertyPlantAndEquipmentGross Property, Plant and Equipment, Gross, Ending Balance Total property, plant and equipment, at cost Mine development us-gaap_Dividends Dividends us-gaap_EquityMethodInvestmentOwnershipPercentage Equity Method Investment, Ownership Percentage Fuel hedge us-gaap_ParticipatingSecuritiesDistributedAndUndistributedEarningsLossBasic Less loss (earnings) allocated to RSUs Derivative Instrument [Axis] Marketable securities - restricted Derivative Contract [Domain] INVESTING ACTIVITIES: Marketable equity securities available for sale, at fair value (restricted)* us-gaap_IncreaseDecreaseInOtherOperatingCapitalNet Other NET INCOME (LOSS) PER SHARE (NOTE 13): Earnings Per Share [Text Block] us-gaap_IncreaseDecreaseInAccruedIncomeTaxesPayable Prepaid income taxes Equity income (loss) - Sunrise Energy Equity (income) loss – Sunrise Energy Accounts payable and accrued liabilities us-gaap_MarketableSecuritiesUnrealizedGainLoss Unrealized gain on marketable securities Investment in Sunrise Energy (Note 15) Equity Method Investments us-gaap_IncomeTaxExpenseBenefit Total income tax expense (benefit) us-gaap_DebtInstrumentUnusedBorrowingCapacityAmount Debt Instrument, Unused Borrowing Capacity, Amount us-gaap_DebtInstrumentIncreaseDecreaseForPeriodNet Debt Instrument, Increase (Decrease), Net, Total Cash and cash equivalents Cash and cash equivalents us-gaap_AllocatedShareBasedCompensationExpense Share-based Payment Arrangement, Expense ARO accretion Certificates of deposit Accretion of ARO Amendment Flag City Area Code New Accounting Pronouncements, Policy [Policy Text Block] us-gaap_GainLossOnSaleOfStockInSubsidiaryOrEquityMethodInvestee Gain on sale of royalty interests in oil properties us-gaap_SharesOutstanding Balance (in shares) Balance (in shares) Common stock, shares outstanding (in shares) Current Fiscal Year End Date us-gaap_DebtInstrumentBasisSpreadOnVariableRate1 Debt Instrument, Basis Spread on Variable Rate Change in estimated fair value us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisWithUnobservableInputs Ending balance, December 31, 2019 Ending balance, June 30, 2020* Weighted average discount rate Document Fiscal Period Focus Document Fiscal Year Focus Lease, Cost [Table Text Block] Document Period End Date Right-of-use assets acquired by operating lease us-gaap_IncreaseDecreaseInPrepaidExpense Prepaid expenses Weighted average remaining lease term in years (Year) Entity File Number Entity Emerging Growth Company Document Type us-gaap_AssetImpairmentCharges Asset Impairment Charges, Total Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block] Entity Small Business Entity Shell Company Document Information [Line Items] Document Information [Table] Entity Filer Category Debt Instrument [Axis] Entity Current Reporting Status Debt Instrument, Name [Domain] London Interbank Offered Rate (LIBOR) [Member] Variable Rate [Domain] Variable Rate [Axis] us-gaap_ConcentrationRiskPercentage1 Concentration Risk, Percentage Entity Tax Identification Number Entity Central Index Key Entity Registrant Name Stock-based compensation Entity [Domain] Legal Entity [Axis] Entity Address, Address Line One Entity Address, City or Town Geographic Concentration Risk [Member] us-gaap_IncreaseDecreaseInAccountsAndNotesReceivable Accounts receivable Entity Address, Postal Zip Code Entity Address, State or Province Concentration Risk Type [Axis] Concentration Risk Type [Domain] Entity Common Stock, Shares Outstanding Revenue from Contract with Customer Benchmark [Member] us-gaap_IncreaseDecreaseInInventories Inventory Trading Symbol Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Domain] Local Phone Number us-gaap_TableTextBlock Notes Tables us-gaap_GainLossOnDispositionOfAssets1 Gain on sale of assets us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity Line of Credit Facility, Maximum Borrowing Capacity Stock issued on vesting of RSUs (in shares) us-gaap_GainLossOnSaleOfProperty Gain on sale of royalty interests in oil properties Stock issued on vesting of RSUs SG&A us-gaap_IncreaseDecreaseInMaterialsAndSupplies Parts and supplies Schedule of Line of Credit Facilities [Table Text Block] us-gaap_LiabilitiesAndStockholdersEquity Total liabilities, redeemable noncontrolling interests, and stockholders’ equity Inventory (Note 3) Retained earnings Exploration costs Debt Disclosure [Text Block] Other us-gaap_InterestExpenseOther Cash and Cash Equivalents [Domain] Interest (1) Total interest (1) Bank interest Change in current assets and liabilities: CASH, CASH EQUIVALENTS, AND RESTRICTED CASH CONSIST OF THE FOLLOWING: Amortization and write off of deferred financing costs Amortization of debt issuance costs Restricted Cash and Cash Equivalents [Axis] us-gaap_DisclosureTextBlockAbstract Notes to Financial Statements Inventory Disclosure [Text Block] Subsequent Event [Member] Other long-term liabilities Total operating lease liability Subsequent Event Type [Axis] Subsequent Event Type [Domain] us-gaap_OperatingLeaseRightOfUseAsset Operating Lease, Right-of-Use Asset us-gaap_LesseeOperatingLeaseLiabilityPaymentsDue Total minimum lease payments us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount Less imputed interest Deferred income taxes Deferred 2023 2024 2021 2022 Lessee, Operating Lease, Liability, Maturity [Table Text Block] us-gaap_ShareBasedCompensation Stock-based compensation Other long-term assets (Note 4) Total other assets 2020 Advanced coal royalties us-gaap_Revenues Total revenue Assets, Fair Value Disclosure DD&A us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation Taxes paid on vesting of RSUs (in shares) us-gaap_AssetsCurrent Total current assets Buildings and equipment Amount before accumulated depreciation of building structures held for productive use and tangible personal property used to produce goods and services. Prepaid income taxes Common stock, $.01 par value, 100,000 shares authorized; 30,465 and 30,420 outstanding, respectively Measurement Frequency [Axis] Measurement Frequency [Domain] Fair Value, Recurring [Member] Common stock, shares authorized (in shares) Fair Value Measurement and Measurement Inputs, Recurring and Nonrecurring [Text Block] Common stock, par value (in dollars per share) Statistical Measurement [Domain] Operating cash outflows from operating leases Maximum [Member] hnrg_NoncashInterestExpenseTotal Total non-cash interest The total amount of non-cash interest expense. SUPPLEMENTAL NON-CASH FLOW INFORMATION: Minimum [Member] Change in interest rate swap valuation Amount of interest expense on change in estimated fair value of interest rate swaps. Fuel Hedge [Member] Represents fuel hedge. Product and Service [Axis] Product and Service [Domain] Statistical Measurement [Axis] Closing of Mine [Member] Represents closing of mine. Investment, Name [Domain] Hourglass Sands [Member] Represents Hourglass Sands. Bulldog Reserves [Member] Represents the Bulldog Reserves. Preferred stock, $.10 par value, 10,000 shares authorized; none issued Preferred stock, shares issued (in shares) Self Insurance [Text Block] The entire disclosure for self insurance. hnrg_EquipmentRedeployed Equipment, Redeployed The amount of equipment to be redeployed. Cash paid for interest Carlisle Mine [Member] Represents Carlisle Mine. Investment, Name [Axis] Prepaid expenses hnrg_DebtInstrumentCovenantMaximumAnnualCapitalExpenditures Debt Instrument, Covenant, Maximum Annual Capital Expenditures The maximum capital expenditures per year under the covenant of the debt instrument. Geographical [Axis] hnrg_DebtInstrumentCovenantMaximumLeverageRatioForDividends Debt Instrument, Covenant, Maximum Leverage Ratio for Dividends The maximum leverage ratio allowed for payment of dividends under covenant of the debt instrument. Geographical [Domain] Preferred stock, shares authorized (in shares) Credit Agreement [Member] Represents the credit agreement. Preferred stock, par value (in dollars per share) Parts and supplies, allowance us-gaap_InventoryAdjustments Inventory Adjustments, Total Term Loan [Member] Represents the term loan. Fair Value, Inputs, Level 3 [Member] Fair Value Hierarchy and NAV [Domain] INDIANA Fair Value, Inputs, Level 1 [Member] Fair Value, Inputs, Level 2 [Member] hnrg_DebtInstrumentLiquidity Debt Instrument, Liquidity The amount of liquidity under the debt instrument. Fair Value Hierarchy and NAV [Axis] Cash received from income taxes hnrg_LeverageRatio Leverage Ratio The leverage ratio. Parts and supplies, net of allowance of $274 hnrg_DebtServiceCoverageRatio Debt Service Coverage Ratio The debt service coverage ratio (consolidated adjusted EBITDA / annual debt service). hnrg_DebtInstrumentVariableRateFloor Debt Instrument, Variable Rate Floor The floor percentage of variable interest rate of the debt instrument. hnrg_DebtInstrumentCovenantMinimumDebtServiceCoverageRatio Debt Instrument, Covenant, Minimum Debt Service Coverage Ratio The minimum debt service coverage ratio (consolidated adjusted EBITDA / annual debt service) under the covenant of the debt instrument. Through December 31, 2020 [Member] Represents through December 31, 2021. OPERATING ACTIVITIES: After December 31, 2021 [Member] Represents after December 31, 2021. Maximum Leverage Ratio The maximum leverage ratio (consolidated funded debt / trailing twelve months adjusted EBITDA) under the covenant of the debt instrument. Periods Ended March 31, 2020 and June 30, 2020 [Member] Represents the period ended March 31, 2020 and June 30, 2020. Periods Ended September 30, 2020 ad December 31, 2020 [Member] Represents the periods ended September 30, 2020 and December 31, 2020. Periods Ended March 31, 2021 and June 30, 2021 [Member] Represents the periods ended March 31, 2021 and June 30, 2021. Statement [Line Items] Current bank debt Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations. Accounts receivable Long-term bank debt Amount before unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations. Additional paid-in capital Miscellaneous The amount of income not otherwise disclosed. Vesting in 2020 [Member] Represents vesting in 2020. Periods Ended September 30, 2021 and December 31, 2021 [Member] Represents the periods ended September 30, 2021 and December 31, 2021. REVENUE: Period Ended March 31, 2022 and Thereafter [Member] Represents the period ended March 31, 2022 and all periods thereafter. Contracts with Price Reopeners [Member] Represents contracts with price reopeners. Stockholders' equity: Future Workers' Compensation Claim Payments [Member] Represents future workers' compensation claim payments hnrg_NumberOfMiningUnits Number of Mining Units The number of mining units. Interest Rate Swap, One [Member] Forward based contracts in which two parties agree to swap periodic payments that are fixed at the outset of the swap contract with variable payments based on a market interest rate (index rate) over a specified period. Vesting in 2021 [Member] Represents vesting in 2021. Vesting in 2022 [Member] Represents vesting in 2022. Long-Lived Tangible Asset [Axis] RSUs vesting (in shares) The number of equity-based payment instruments, excluding stock (or unit) options, that are vest in a future period. Long-Lived Tangible Asset [Domain] Buildings and Equipment [Member] Represents buildings and equipment. Other us-gaap_OtherAssetsMiscellaneousNoncurrent Interest Rate Swap, Two [Member] Forward based contracts in which two parties agree to swap periodic payments that are fixed at the outset of the swap contract with variable payments based on a market interest rate (index rate) over a specified period. Current assets: Sunrise Energy, LLC [Member] Represents Sunrise Energy, LLC. Schedule of Other Assets, Noncurrent [Table Text Block] us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents Cash, cash equivalents, and restricted cash, beginning of period Cash, cash equivalents, and restricted cash, end of period Redeemable noncontrolling interests (Note 2) us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect Decrease in cash, cash equivalents, and restricted cash us-gaap_NetCashProvidedByUsedInFinancingActivities Cash used in financing activities us-gaap_Liabilities Total liabilities Other operating income (Note 8) Other Operating Income Asset retirement obligations (ARO) Cash provided by operating activities us-gaap_NetCashProvidedByUsedInInvestingActivities Cash used in investing activities Operating costs and expenses Deferred income taxes Other Operating Income and Expense [Text Block] Derivative liabilities us-gaap_AccountsPayableAndAccruedLiabilitiesCurrentAndNoncurrent Total accounts payable and accrued liabilities Accrued property taxes Accounts payable us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation Taxes paid on vesting of RSUs Workers' compensation reserve Equity Method Investments and Joint Ventures Disclosure [Text Block] us-gaap_PaymentsOfDividendsCommonStock Dividends Accrued payroll Group health insurance Other us-gaap_OtherAccruedLiabilitiesCurrentAndNoncurrent us-gaap_CostsAndExpenses Total costs and expenses COSTS AND EXPENSES: Scenario [Domain] Retained Earnings [Member] Coal sales Scenario [Axis] Additional Paid-in Capital [Member] Common Stock [Member] Equity Components [Axis] Equity Component [Domain] us-gaap_LongTermDebt Net bank debt Current us-gaap_RevenueRemainingPerformanceObligationPercentage Revenue, Remaining Performance Obligation, Percentage us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1 Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period (Year) us-gaap_RevenueRemainingPerformanceObligation Revenue, Remaining Performance Obligation, Amount INCOME TAX EXPENSE (BENEFIT) (NOTE 9): Other Noncurrent Liabilities [Member] us-gaap_NotesPayable Notes Payable, Total Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis] us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest INCOME (LOSS) BEFORE INCOME TAXES Mining Properties and Mineral Rights [Member] us-gaap_LineOfCredit Long-term Line of Credit, Total us-gaap_PaymentsOfDebtIssuanceCosts Debt issuance costs us-gaap_DeferredFinanceCostsNoncurrentNet Less unamortized debt issuance cost us-gaap_DeferredFinanceCostsNet Debt Issuance Costs, Net, Total Less total unamortized debt issuance cost us-gaap_DeferredFinanceCostsCurrentNet Less unamortized debt issuance cost Revenue from Contract with Customer [Text Block] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Document Quarterly Report Entity Incorporation, State or Country Code Total bank debt Long-term Debt, Gross Accounting Policies [Abstract] Significant Accounting Policies [Text Block] Document Transition Report Entity Interactive Data Current Security Exchange Name Title of 12(b) Security hnrg_GeographicSpreadOfMiningUnitsInMiles Area of Real Estate Property Total active underground mining miles with equipment that is self-insured. Schedule of Other Operating Income (Expense) [Table Text Block] The tabular disclosure for other operating income and expenses. Paycheck Protection Program CARES Act [Member] Represents loan designed to provide funds for small businesses to keep their employees on the payroll. us-gaap_DerivativeAmountOfHedgedItem Derivative, Amount of Hedged Item Government imposition reimbursements Represents government imposition reimbursements income. Coal storage Represents coal storage income. us-gaap_RepaymentsOfBankDebt Payments on bank debt Basic and diluted (in shares) us-gaap_SharePrice Share Price (in dollars per share) Proceeds from PPP loan Proceeds from Notes Payable, Total Basic and diluted (in dollars per share) Borrowings of bank debt Statement [Table] Statement of Financial Position [Abstract] Accounts Payable and Accrued Liabilities Disclosure [Text Block] us-gaap_EffectiveIncomeTaxRateContinuingOperations Effective Income Tax Rate Reconciliation, Percent, Total Contract with Customer, Basis of Pricing [Axis] Statement of Cash Flows [Abstract] Contract with Customer, Basis of Pricing [Domain] hnrg_DebtInstrumentInterestRateEffectivePercentageUnhedgedAmount Debt Instrument, Interest Rate, Effective Percentage Unhedged Amount Represents effective percentage unhedged amount of interest rate for debt instrument. Fixed-price Contract [Member] Statement of Stockholders' Equity [Abstract] Income Statement [Abstract] us-gaap_LesseeOperatingLeaseRemainingLeaseTerm Lessee, Operating Lease, Remaining Lease Term (Year) hnrg_DebtInstrumentUnhedgedPortion Debt Instrument, Unhedged Portion Represents ungedged portion of debt instrument. Land and mineral rights us-gaap_MineralPropertiesNet Mineral Properties, Net, Total Schedule of Accounts Payable and Accrued Liabilities [Table Text Block] us-gaap_RestructuringAndRelatedCostExpectedCost1 Restructuring and Related Cost, Expected Cost, Total us-gaap_RestructuringAndRelatedCostIncurredCost Restructuring and Related Costs, Incurred Cost, Total us-gaap_DerivativeBasisSpreadOnVariableRate Derivative, Basis Spread on Variable Rate Type of Restructuring [Domain] us-gaap_LiabilitiesNoncurrent Total long-term liabilities Restructuring Type [Axis] FINANCING ACTIVITIES: Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Other us-gaap_StockholdersEquity Total stockholders’ equity Balance Balance Class of Stock [Axis] us-gaap_LongTermDebtNoncurrent Net long-term portion Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Interest Rate Swap [Member] PPP note (Note 5) us-gaap_DerivativeFixedInterestRate Derivative, Fixed Interest Rate