Self Insurance (Details) $ in Millions	Mar. 31, 2016 site mi	Aug. 31, 2010 USD ($)
Self Insurance [Abstract]
Number of mining units with self-insured equipment \| site	10
Area of self-insured mining units \| mi	20
Mining equipment at historical cost \| $		$ 255

Total active underground mining miles with equipment that is self-insured.

No definition available.

Name:	hnrg_GeorgraphicSpreadOfMiningUnits
Namespace Prefix:	hnrg_
Data Type:	num:lengthItemType
Balance Type:	na
Period Type:	instant