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v3.7.0.1

Self Insurance (Details) $ in Millions | Dec. 31, 2016 item mi | Aug. 31, 2010 USD ($)
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Property, Plant and Equipment [Line Items] |  |
Area of self-insured mining units | mi | 18 |
Mining equipment at historical cost | $ |  | $ 248
High Efficiency Units [Member] |  |
Property, Plant and Equipment [Line Items] |  |
Number of mining units with self-insured equipment | item | 10 |

X
- 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

X
- 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 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

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + 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: |