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Equity Investment in Savoy (Narrative) (Details) (USD $) | 1 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Oct. 31, 2014 | Dec. 31, 2014 | Dec. 31, 2013 | Sep. 30, 2014
Cash distributions | $ 4,900,000 us-gaap_EquityMethodInvestmentDividendsOrDistributions | $ 8,109,000 us-gaap_EquityMethodInvestmentDividendsOrDistributions | $ 1,325,000 us-gaap_EquityMethodInvestmentDividendsOrDistributions |
Minimum prior industry experience of petroleum engineering consultant |  | 5 years |  |
Savoy [Member] |  |  |  |
Equity method investment ownership percentage |  | 40.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / dei_LegalEntityAxis = hnrg_SavoyMember |  | 45.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / dei_LegalEntityAxis = hnrg_SavoyMember
Cash distributions paid | $ 12,000,000 us-gaap_DistributionMadeToLimitedPartnerCashDistributionsPaid / dei_LegalEntityAxis = hnrg_SavoyMember |  |  |

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- Definition Amount of cash distribution paid to unit-holder of limited partnership (LP). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 272 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70478-108055 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 272 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70434-108055 + Details
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- Definition The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6382943&loc=d3e33918-111571 + Details
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