Percentage of revenue expected to be recognized by set date

No definition available.

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Period Type:	instant

- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6351-108592

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13531-108611

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13537-108611

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6404-108592

+ Details

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of transaction price allocated to performance obligation that has not been recognized as revenue.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130556-203045

+ Details

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

- Definition

Description of when remaining performance obligation is expected to be recognized as revenue.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (b)(2)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130556-203045

+ Details

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

- Definition

Year in which remaining performance obligation is expected to be recognized, in CCYY format.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130556-203045

+ Details

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Balance Type:	na
Period Type:	instant

- Details

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- Details

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- Details

Name:	us-gaap_ContractWithCustomerBasisOfPricingAxis=us-gaap_FixedPriceContractMember
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Data Type:	na
Balance Type:
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- Details

Name:	us-gaap_ContractWithCustomerBasisOfPricingAxis=hnrg_IndexPricedContractsMember
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Revenue (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
Revenue (Narrative) (Details) - USD ($) $ in Millions	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Sep. 30, 2018
Sales Revenue, Net [Member] \| Indiana [Member]
Percentage of revenue	70.00%	72.00%	67.00%	70.00%
Fixed-price Contract [Member]
Performance obligation	$ 684		$ 684
Percentage of revenue expected to be recognized by set date	61.00%		61.00%
Revenue, remaining performance obligation, expected timing of satisfaction, year	2020		2020
Revenue, remaining performance obligation, expected timing of satisfaction, explanation			We expect to recognize approximately 61% of this revenue through 2020, with the remainder recognized thereafter.
Index Priced Contracts [Member]
Performance obligation	$ 330		$ 330
Revenue, remaining performance obligation, expected timing of satisfaction, year					2020
Revenue, remaining performance obligation, expected timing of satisfaction, explanation			We expect to recognize all of this revenue beginning in 2020.