Note 9 - Stock Compensation Plans - Vesting of Non-vested RSU Grants (Details)	Mar. 31, 2022 shares
Restricted Stock Units (RSUs) [Member] \| Vesting in 2023 [Member]
RSUs vesting (in shares)	188,500

The number of equity-based payment instruments, excluding stock (or unit) options, that are vest in a future period.

No definition available.

Name:	hnrg_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestingInFuturePeriod
Namespace Prefix:	hnrg_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant