Amount of debt with maximum interest rate

No definition available.

Name:	hnrg_AmountOfDebtWithMaximumInterestRate
Namespace Prefix:	hnrg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Debt service coverage ratio

+ References

No definition available.

+ Details

Name:	hnrg_DebtServiceCoverageRatio
Namespace Prefix:	hnrg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Leverage Ratio

+ References

No definition available.

+ Details

Name:	hnrg_LeverageRatio
Namespace Prefix:	hnrg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Leverage ratio threshold

+ References

No definition available.

+ Details

Name:	hnrg_LeverageRatioThreshold
Namespace Prefix:	hnrg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Liquidity

+ References

No definition available.

+ Details

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

- Definition

Period of extension of debt instrument maturity date

+ References

No definition available.

+ Details

Name:	hnrg_PeriodOfExtensionOfDebtInstrumentMaturityDate
Namespace Prefix:	hnrg_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of amortization expense attributable to debt issuance costs.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(8))
-URI http://asc.fasb.org/extlink&oid=115205541&loc=SL114868664-224227

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28555-108399

+ Details

Name:	us-gaap_AmortizationOfFinancingCosts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of the fee that accompanies borrowing money under the debt instrument.

+ References

+ Details

Name:	us-gaap_DebtInstrumentFeeAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6036836-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateEffectivePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Incremental percentage increase (decrease) in the stated rate on a debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentInterestRateIncreaseDecrease
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of unused borrowing capacity under the long-term financing arrangement that is available to the entity as of the balance sheet date.

+ References

+ Details

Name:	us-gaap_DebtInstrumentUnusedBorrowingCapacityAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28555-108399

+ Details

Name:	us-gaap_DeferredFinanceCostsNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value of the amount outstanding under the credit facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13433-108611

+ Details

Name:	us-gaap_LineOfCreditFacilityFairValueOfAmountOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_DebtInstrumentAxis=hnrg_CreditAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=hnrg_TermLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Bank Debt (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
Bank Debt (Narrative) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Amortization of debt issuance costs			$ 2,095	$ 2,024
Leverage ratio			2.62%
Leverage ratio threshold			250.00%
Debt service coverage ratio			184.00%
Debt, interest rate spread on variable rate		3.50%	3.00%
Interest rate effective percentage	6.42%	6.42%	5.92%
Credit Agreement [Member]
Debt Instrument [Line Items]
Deferred financing costs expensed			$ 6,500	$ 7,400
Credit agreement, amount outstanding			180,000
Borrowing capacity			26,000
Liquidity			$ 35,000
Interest rate increase (decrease)	(0.50%)
Period of extension of debt instrument maturity date	16 months
London Interbank Offered Rate (LIBOR) [Member] \| Minimum [Member] \| Credit Agreement [Member]
Debt Instrument [Line Items]
Debt, interest rate spread on variable rate			2.25%
London Interbank Offered Rate (LIBOR) [Member] \| Maximum [Member] \| Credit Agreement [Member]
Debt Instrument [Line Items]
Debt, interest rate spread on variable rate			4.00%
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 120,000
Credit agreement, amount outstanding			77,000
Debt issuance costs			7,200
Amount of debt with maximum interest rate			$ 53,000
Revolving Credit Facility [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Debt service coverage ratio			125.00%
Term Loan [Member]
Debt Instrument [Line Items]
Credit agreement, amount outstanding			$ 103,000