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Note 12 - Fair Value Measurements (Details Textual) - USD ($) $ in Millions | Jun. 30, 2024 | Dec. 31, 2023
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Cash and Cash Equivalents, Restricted Cash Balances, Deposits | $ 10.7 | $ 7.1

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- Definition The cash equivalents and restricted cash related to deposits. + References No definition available. + Details
Name: | hnrg_CashAndCashEquivalentsRestrictedCashBalancesDeposits
Namespace Prefix: | hnrg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant