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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

X
- Definition The number of equity-based payment instruments, excluding stock (or unit) options, that are to vest in a future period. + References No definition available. + Details
Name: | hnrg_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestingInFuturePeriod
Namespace Prefix: | hnrg_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | us-gaap_VestingAxis=hnrg_VestingIn2024Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AwardTypeAxis=us-gaap_RestrictedStockUnitsRSUMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_VestingAxis=hnrg_RepresentsVestingIn2025Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |