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Note 10 - Stock Compensation Plans - Vesting of Non-vested RSU Grants (Details) - Restricted Stock Units (RSUs) [Member] | Dec. 31, 2020 shares
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RSUs vesting (in shares) | 324,250
Vesting in 2021 [Member] |
RSUs vesting (in shares) | 305,250
Vesting in 2022 [Member] |
RSUs vesting (in shares) | 9,000
Vesting in 2023 [Member] |
RSUs vesting (in shares) | 10,000

X
- Definition The number of equity-based payment instruments, excluding stock (or unit) options, that are 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_AwardTypeAxis=us-gaap_RestrictedStockUnitsRSUMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_VestingAxis=hnrg_VestingIn2021Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_VestingAxis=hnrg_VestingIn2022Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_VestingAxis=hnrg_VestingIn2023Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |