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Self Insurance (Details) (USD $) In Millions, unless otherwise specified | Sep. 30, 2014 mi site | Aug. 31, 2010
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Self Insurance [Abstract] |  |
Number of mining units with self-insured equipment | 13 |
Area of self-insured mining units | 23 |
Mining equipment at historical cost |  | $ 245

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- Definition Total active underground mining miles with equipment that is self-insured. + References No definition available. + Details
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Balance Type: | na
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- Definition Value of underground mining equipment + References No definition available. + Details
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Namespace Prefix: | hnrg_
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Balance Type: | credit
Period Type: | instant

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

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- Details
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Namespace Prefix: | hnrg_
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