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FAIR VALUE MEASUREMENTS (Details) - USD ($) $ in Millions | Sep. 30, 2024 | Dec. 31, 2023
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FAIR VALUE MEASUREMENTS |  |
Total cash and cash equivalent and restricted cash balances on deposit with financial institutions | $ 9.6 | $ 7.1

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

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
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Balance Type: | na
Period Type: | duration