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Self Insurance (Details) (USD $) In Millions, unless otherwise specified | Dec. 31, 2014 site property mi | Aug. 31, 2010
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Property, Plant and Equipment [Line Items] |  |
Number of mines with self-insured mining equipment | 3 hnrg_NumberOfMinesWithSelfInsuredMiningEquipment |
Area of self-insured mining units | 30 hnrg_GeorgraphicSpreadOfMiningUnits |
Number of locations with self-insured mining equipment | 11 hnrg_NumberOfLocationsWithSelfInsuredMiningEquipment |
Mining equipment at historical cost |  | $ 246 hnrg_MiningEquipmentAtHistoricalCost
High Efficiency Units [Member] |  |
Property, Plant and Equipment [Line Items] |  |
Number of mining units with self-insured equipment | 11 hnrg_NumberOfMiningUnits / us-gaap_PropertyPlantAndEquipmentByTypeAxis = hnrg_HighEfficiencyUnitsMember |

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- Definition Total active underground mining miles with equipment that is self-insured. + References No definition available. + Details
Name: | hnrg_GeorgraphicSpreadOfMiningUnits
Namespace Prefix: | hnrg_
Data Type: | num:lengthItemType
Balance Type: | na
Period Type: | instant

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- Definition Value of underground mining equipment + References No definition available. + Details
Name: | hnrg_MiningEquipmentAtHistoricalCost
Namespace Prefix: | hnrg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Number of locations with self-insured mining equipment + References No definition available. + Details
Name: | hnrg_NumberOfLocationsWithSelfInsuredMiningEquipment
Namespace Prefix: | hnrg_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number of mines with self-insured mining equipment + References No definition available. + Details
Name: | hnrg_NumberOfMinesWithSelfInsuredMiningEquipment
Namespace Prefix: | hnrg_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number of underground mining units in which underground equipment is self-insured. + References No definition available. + Details
Name: | hnrg_NumberOfMiningUnits
Namespace Prefix: | hnrg_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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- Details
Name: | us-gaap_PropertyPlantAndEquipmentLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_PropertyPlantAndEquipmentByTypeAxis=hnrg_HighEfficiencyUnitsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |