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Equity Investment in Savoy (Proved Reserves Cash Flows) (Details) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013
Future cash inflows: |  |
Cash inflows | $ 63,738 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows | $ 147,805 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows
Future production costs | (16,635)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureProductionCosts1 | (24,446)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureProductionCosts1
Future development costs | (1,850)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureDevelopmentCosts1 | (3,073)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureDevelopmentCosts1
Future income tax (none since Savoy is a pass-through entity for income tax purposes) |  |
Future net cash flows | 45,253 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureNetCashFlows | 120,286 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureNetCashFlows
10% annual discount for estimated timing of cash flows | (11,153)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves10PercentAnnualDiscountForEstimatedTimingOfCashFlows | (29,486)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves10PercentAnnualDiscountForEstimatedTimingOfCashFlows
Standardized measure of discounted future net cash flows | 34,100 us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves | 90,800 us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves
Oil [Member] |  |
Future cash inflows: |  |
Cash inflows | 60,190 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_OilReservesMember | 141,244 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_OilReservesMember
Natural Gas Liquids [Member] |  |
Future cash inflows: |  |
Cash inflows | 1,624 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_NaturalGasLiquidsReservesMember | 4,220 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_NaturalGasLiquidsReservesMember
Natural Gas [Member] |  |
Future cash inflows: |  |
Cash inflows | 1,924 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_NaturalGasReservesMember | 2,341 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_NaturalGasReservesMember
Proved Developed [Member] |  |
Future cash inflows: |  |
Cash inflows | 44,119 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / hnrg_ProvedReserveAxis = hnrg_ProvedDevelopedMember | 74,498 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / hnrg_ProvedReserveAxis = hnrg_ProvedDevelopedMember
Future production costs | (12,886)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureProductionCosts1 / hnrg_ProvedReserveAxis = hnrg_ProvedDevelopedMember | (12,213)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureProductionCosts1 / hnrg_ProvedReserveAxis = hnrg_ProvedDevelopedMember
Future development costs | (60)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureDevelopmentCosts1 / hnrg_ProvedReserveAxis = hnrg_ProvedDevelopedMember |
Future income tax (none since Savoy is a pass-through entity for income tax purposes) |  |
Future net cash flows | 31,173 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureNetCashFlows / hnrg_ProvedReserveAxis = hnrg_ProvedDevelopedMember | 62,285 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureNetCashFlows / hnrg_ProvedReserveAxis = hnrg_ProvedDevelopedMember
10% annual discount for estimated timing of cash flows | (7,125)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves10PercentAnnualDiscountForEstimatedTimingOfCashFlows / hnrg_ProvedReserveAxis = hnrg_ProvedDevelopedMember | (14,375)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves10PercentAnnualDiscountForEstimatedTimingOfCashFlows / hnrg_ProvedReserveAxis = hnrg_ProvedDevelopedMember
Standardized measure of discounted future net cash flows | 24,048 us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves / hnrg_ProvedReserveAxis = hnrg_ProvedDevelopedMember | 47,910 us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves / hnrg_ProvedReserveAxis = hnrg_ProvedDevelopedMember
Proved Developed [Member] | Oil [Member] |  |
Future cash inflows: |  |
Cash inflows | 41,660 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / hnrg_ProvedReserveAxis = hnrg_ProvedDevelopedMember / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_OilReservesMember | 70,582 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / hnrg_ProvedReserveAxis = hnrg_ProvedDevelopedMember / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_OilReservesMember
Proved Developed [Member] | Natural Gas Liquids [Member] |  |
Future cash inflows: |  |
Cash inflows | 1,256 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / hnrg_ProvedReserveAxis = hnrg_ProvedDevelopedMember / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_NaturalGasLiquidsReservesMember | 2,551 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / hnrg_ProvedReserveAxis = hnrg_ProvedDevelopedMember / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_NaturalGasLiquidsReservesMember
Proved Developed [Member] | Natural Gas [Member] |  |
Future cash inflows: |  |
Cash inflows | 1,203 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / hnrg_ProvedReserveAxis = hnrg_ProvedDevelopedMember / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_NaturalGasReservesMember | 1,365 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / hnrg_ProvedReserveAxis = hnrg_ProvedDevelopedMember / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_NaturalGasReservesMember
Proved Undeveloped (PUDs) [Member] |  |
Future cash inflows: |  |
Cash inflows | 19,619 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / hnrg_ProvedReserveAxis = hnrg_ProvedUndevelopedMember | 73,307 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / hnrg_ProvedReserveAxis = hnrg_ProvedUndevelopedMember
Future production costs | (3,749)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureProductionCosts1 / hnrg_ProvedReserveAxis = hnrg_ProvedUndevelopedMember | (12,233)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureProductionCosts1 / hnrg_ProvedReserveAxis = hnrg_ProvedUndevelopedMember
Future development costs | (1,790)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureDevelopmentCosts1 / hnrg_ProvedReserveAxis = hnrg_ProvedUndevelopedMember | (3,073)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureDevelopmentCosts1 / hnrg_ProvedReserveAxis = hnrg_ProvedUndevelopedMember
Future income tax (none since Savoy is a pass-through entity for income tax purposes) |  |
Future net cash flows | 14,080 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureNetCashFlows / hnrg_ProvedReserveAxis = hnrg_ProvedUndevelopedMember | 58,001 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureNetCashFlows / hnrg_ProvedReserveAxis = hnrg_ProvedUndevelopedMember
10% annual discount for estimated timing of cash flows | (4,028)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves10PercentAnnualDiscountForEstimatedTimingOfCashFlows / hnrg_ProvedReserveAxis = hnrg_ProvedUndevelopedMember | (15,111)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves10PercentAnnualDiscountForEstimatedTimingOfCashFlows / hnrg_ProvedReserveAxis = hnrg_ProvedUndevelopedMember
Standardized measure of discounted future net cash flows | 10,052 us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves / hnrg_ProvedReserveAxis = hnrg_ProvedUndevelopedMember | 42,890 us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves / hnrg_ProvedReserveAxis = hnrg_ProvedUndevelopedMember
Proved Undeveloped (PUDs) [Member] | Oil [Member] |  |
Future cash inflows: |  |
Cash inflows | 18,530 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / hnrg_ProvedReserveAxis = hnrg_ProvedUndevelopedMember / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_OilReservesMember | 70,662 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / hnrg_ProvedReserveAxis = hnrg_ProvedUndevelopedMember / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_OilReservesMember
Proved Undeveloped (PUDs) [Member] | Natural Gas Liquids [Member] |  |
Future cash inflows: |  |
Cash inflows | 368 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / hnrg_ProvedReserveAxis = hnrg_ProvedUndevelopedMember / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_NaturalGasLiquidsReservesMember | 1,669 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / hnrg_ProvedReserveAxis = hnrg_ProvedUndevelopedMember / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_NaturalGasLiquidsReservesMember
Proved Undeveloped (PUDs) [Member] | Natural Gas [Member] |  |
Future cash inflows: |  |
Cash inflows | 721 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / hnrg_ProvedReserveAxis = hnrg_ProvedUndevelopedMember / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_NaturalGasReservesMember | 976 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / hnrg_ProvedReserveAxis = hnrg_ProvedUndevelopedMember / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_NaturalGasReservesMember
NYMEX Strip Prices [Member] |  |
Future cash inflows: |  |
Cash inflows | 39,642 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / hnrg_UnderlyingBasisAxis = hnrg_NymexStripPricesMember |
Future production costs | (12,860)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureProductionCosts1 / hnrg_UnderlyingBasisAxis = hnrg_NymexStripPricesMember |
Future development costs | (1,858)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureDevelopmentCosts1 / hnrg_UnderlyingBasisAxis = hnrg_NymexStripPricesMember |
Future income tax (none since Savoy is a pass-through entity for income tax purposes) |  |
Future net cash flows | 24,924 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureNetCashFlows / hnrg_UnderlyingBasisAxis = hnrg_NymexStripPricesMember |
10% annual discount for estimated timing of cash flows | (5,944)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves10PercentAnnualDiscountForEstimatedTimingOfCashFlows / hnrg_UnderlyingBasisAxis = hnrg_NymexStripPricesMember |
Standardized measure of discounted future net cash flows | 18,980 us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves / hnrg_UnderlyingBasisAxis = hnrg_NymexStripPricesMember |
NYMEX Strip Prices [Member] | Oil [Member] |  |
Future cash inflows: |  |
Cash inflows | 37,007 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_OilReservesMember / hnrg_UnderlyingBasisAxis = hnrg_NymexStripPricesMember |
NYMEX Strip Prices [Member] | Natural Gas Liquids [Member] |  |
Future cash inflows: |  |
Cash inflows | 1,037 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_NaturalGasLiquidsReservesMember / hnrg_UnderlyingBasisAxis = hnrg_NymexStripPricesMember |
NYMEX Strip Prices [Member] | Natural Gas [Member] |  |
Future cash inflows: |  |
Cash inflows | 1,598 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_NaturalGasReservesMember / hnrg_UnderlyingBasisAxis = hnrg_NymexStripPricesMember |
NYMEX Strip Prices [Member] | Proved Developed [Member] |  |
Future cash inflows: |  |
Cash inflows | 26,468 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / hnrg_ProvedReserveAxis = hnrg_ProvedDevelopedMember / hnrg_UnderlyingBasisAxis = hnrg_NymexStripPricesMember |
Future production costs | (9,462)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureProductionCosts1 / hnrg_ProvedReserveAxis = hnrg_ProvedDevelopedMember / hnrg_UnderlyingBasisAxis = hnrg_NymexStripPricesMember |
Future development costs | (58)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureDevelopmentCosts1 / hnrg_ProvedReserveAxis = hnrg_ProvedDevelopedMember / hnrg_UnderlyingBasisAxis = hnrg_NymexStripPricesMember |
Future income tax (none since Savoy is a pass-through entity for income tax purposes) |  |
Future net cash flows | 16,948 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureNetCashFlows / hnrg_ProvedReserveAxis = hnrg_ProvedDevelopedMember / hnrg_UnderlyingBasisAxis = hnrg_NymexStripPricesMember |
10% annual discount for estimated timing of cash flows | (3,608)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves10PercentAnnualDiscountForEstimatedTimingOfCashFlows / hnrg_ProvedReserveAxis = hnrg_ProvedDevelopedMember / hnrg_UnderlyingBasisAxis = hnrg_NymexStripPricesMember |
Standardized measure of discounted future net cash flows | 13,340 us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves / hnrg_ProvedReserveAxis = hnrg_ProvedDevelopedMember / hnrg_UnderlyingBasisAxis = hnrg_NymexStripPricesMember |
NYMEX Strip Prices [Member] | Proved Developed [Member] | Oil [Member] |  |
Future cash inflows: |  |
Cash inflows | 24,768 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / hnrg_ProvedReserveAxis = hnrg_ProvedDevelopedMember / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_OilReservesMember / hnrg_UnderlyingBasisAxis = hnrg_NymexStripPricesMember |
NYMEX Strip Prices [Member] | Proved Developed [Member] | Natural Gas Liquids [Member] |  |
Future cash inflows: |  |
Cash inflows | 785 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / hnrg_ProvedReserveAxis = hnrg_ProvedDevelopedMember / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_NaturalGasLiquidsReservesMember / hnrg_UnderlyingBasisAxis = hnrg_NymexStripPricesMember |
NYMEX Strip Prices [Member] | Proved Developed [Member] | Natural Gas [Member] |  |
Future cash inflows: |  |
Cash inflows | 915 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / hnrg_ProvedReserveAxis = hnrg_ProvedDevelopedMember / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_NaturalGasReservesMember / hnrg_UnderlyingBasisAxis = hnrg_NymexStripPricesMember |
NYMEX Strip Prices [Member] | Proved Undeveloped (PUDs) [Member] |  |
Future cash inflows: |  |
Cash inflows | 13,174 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / hnrg_ProvedReserveAxis = hnrg_ProvedUndevelopedMember / hnrg_UnderlyingBasisAxis = hnrg_NymexStripPricesMember |
Future production costs | (3,398)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureProductionCosts1 / hnrg_ProvedReserveAxis = hnrg_ProvedUndevelopedMember / hnrg_UnderlyingBasisAxis = hnrg_NymexStripPricesMember |
Future development costs | (1,800)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureDevelopmentCosts1 / hnrg_ProvedReserveAxis = hnrg_ProvedUndevelopedMember / hnrg_UnderlyingBasisAxis = hnrg_NymexStripPricesMember |
Future income tax (none since Savoy is a pass-through entity for income tax purposes) |  |
Future net cash flows | 7,976 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureNetCashFlows / hnrg_ProvedReserveAxis = hnrg_ProvedUndevelopedMember / hnrg_UnderlyingBasisAxis = hnrg_NymexStripPricesMember |
10% annual discount for estimated timing of cash flows | (2,336)us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves10PercentAnnualDiscountForEstimatedTimingOfCashFlows / hnrg_ProvedReserveAxis = hnrg_ProvedUndevelopedMember / hnrg_UnderlyingBasisAxis = hnrg_NymexStripPricesMember |
Standardized measure of discounted future net cash flows | 5,640 us-gaap_StandardizedMeasureOfDiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReserves / hnrg_ProvedReserveAxis = hnrg_ProvedUndevelopedMember / hnrg_UnderlyingBasisAxis = hnrg_NymexStripPricesMember |
NYMEX Strip Prices [Member] | Proved Undeveloped (PUDs) [Member] | Oil [Member] |  |
Future cash inflows: |  |
Cash inflows | 12,239 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / hnrg_ProvedReserveAxis = hnrg_ProvedUndevelopedMember / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_OilReservesMember / hnrg_UnderlyingBasisAxis = hnrg_NymexStripPricesMember |
NYMEX Strip Prices [Member] | Proved Undeveloped (PUDs) [Member] | Natural Gas Liquids [Member] |  |
Future cash inflows: |  |
Cash inflows | 252 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / hnrg_ProvedReserveAxis = hnrg_ProvedUndevelopedMember / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_NaturalGasLiquidsReservesMember / hnrg_UnderlyingBasisAxis = hnrg_NymexStripPricesMember |
NYMEX Strip Prices [Member] | Proved Undeveloped (PUDs) [Member] | Natural Gas [Member] |  |
Future cash inflows: |  |
Cash inflows | $ 683 us-gaap_DiscountedFutureNetCashFlowsRelatingToProvedOilAndGasReservesFutureCashInflows / hnrg_ProvedReserveAxis = hnrg_ProvedUndevelopedMember / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_NaturalGasReservesMember / hnrg_UnderlyingBasisAxis = hnrg_NymexStripPricesMember |

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- Definition This is the amount that is derived from using a discount rate of ten percent a year to reflect the timing of the future net cash flows relating to proved oil and gas reserves. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 30 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62424-109447 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 31 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62455-109447 + Details
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- Definition Amount of estimated future cash inflows from sale of proved oil and gas reserves. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 30 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62424-109447 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 31 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62455-109447 + Details
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- Definition Amount of estimated future cost to be incurred in developing proved oil and gas reserves. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 30 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62424-109447 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 31 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62455-109447 + Details
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- Definition Amount of estimated future income tax expense to be incurred based on the future income less future expense derived from production and sale of proved oil and gas reserves. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 30 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62424-109447 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 31 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62455-109447 + Details
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- Definition Amount of estimated net future cash inflows, after subtracting future development and production costs and future income tax expenses, from sale of proved oil and gas reserves. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 30 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62424-109447 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 31 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62455-109447 + Details
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