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Equity Investment in Savoy (Schedule of Costs Incurred) (Details) (Savoy [Member], USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Savoy [Member]
   
Unproved property acquisition $ 899us-gaap_PaymentsToAcquireOtherPropertyPlantAndEquipment
/ dei_LegalEntityAxis
= hnrg_SavoyMember
$ 1,287us-gaap_PaymentsToAcquireOtherPropertyPlantAndEquipment
/ dei_LegalEntityAxis
= hnrg_SavoyMember
Development 1,224hnrg_OilGasDevelopment
/ dei_LegalEntityAxis
= hnrg_SavoyMember
858hnrg_OilGasDevelopment
/ dei_LegalEntityAxis
= hnrg_SavoyMember
Exploration 5,130us-gaap_ExplorationExpense
/ dei_LegalEntityAxis
= hnrg_SavoyMember
7,061us-gaap_ExplorationExpense
/ dei_LegalEntityAxis
= hnrg_SavoyMember
Total $ 7,253us-gaap_CostsIncurredOilAndGasPropertyAcquisitionExplorationAndDevelopmentActivities
/ dei_LegalEntityAxis
= hnrg_SavoyMember
$ 9,206us-gaap_CostsIncurredOilAndGasPropertyAcquisitionExplorationAndDevelopmentActivities
/ dei_LegalEntityAxis
= hnrg_SavoyMember