Self Insurance (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015 mi site	Aug. 31, 2010
Self Insurance [Abstract]
Number of mining units with self-insured equipment	13hnrg_NumberOfMiningUnits
Area of self-insured mining units	20hnrg_GeorgraphicSpreadOfMiningUnits
Mining equipment at historical cost		$ 250hnrg_MiningEquipmentAtHistoricalCost

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