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

The cash equivalents and restricted cash related to deposits.

No definition available.

Name:	hnrg_CashAndCashEquivalentsRestrictedCashBalancesDeposits
Namespace Prefix:	hnrg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant