Note 8 - Stock Compensation Plans - Vesting of Non-vested RSU Grants (Details) - Restricted Stock Units (RSUs) [Member]	Dec. 31, 2023 shares
Vesting in 2024 [Member]
RSUs vesting (in shares)	319,419
Represents vesting in 2025 [Member]
RSUs vesting (in shares)	538,944

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

No definition available.

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