Amount of increase (decrease) in standardized measure of discounted future net cash flow as a result of passage of time.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 235

-Section 50

-Paragraph 35

-Subparagraph (h)

-URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62500-109447

+ Details

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

- Definition

The revenues derived from sales of oil or gas in each geographic area during the reporting period divided by the number of barrels of oil produced or thousands of cubic feet of gas produced.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Industry Guide

-Number 2

-Paragraph 3

-Subparagraph A

+ Details

Name:	us-gaap_AverageSalesPrices
Namespace Prefix:	us-gaap_
Data Type:	us-types:perUnitItemType
Balance Type:	na
Period Type:	duration

- Definition

The aggregate carrying amount as of the balance sheet date of unrefined petroleum and the liquid hydrocarbon components recovered from natural gas.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.6(a))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 6

-Subparagraph a

-Article 5

+ Details

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

- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 323

-SubTopic 10

-Section 50

-Paragraph 3

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=6382943&loc=d3e33918-111571

+ Details

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

- Definition

Amount of increase (decrease) in standardized measure of discounted future net cash flow as a result of extensions, discoveries and improved recovery of proved oil and gas reserves.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 235

-Section 50

-Paragraph 35

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62500-109447

+ Details

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

- Definition

Amount of increase (decrease) in standardized measure of discounted future net cash flow as a result of change in estimated future development costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 235

-Section 50

-Paragraph 31

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62455-109447

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 235

-Section 50

-Paragraph 35

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62500-109447

+ Details

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

- Definition

Amount of increase (decrease) in standardized measure of discounted future net cash flow as a result of change in sales and transfer prices and in production (lifting) costs related to future production.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 235

-Section 50

-Paragraph 35

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62500-109447

+ Details

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

- Details

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

- Definition

Amount of increase (decrease) in standardized measure of discounted future net cash flow as a result of revisions of estimated quantity of oil and gas in proved reserves.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 235

-Section 50

-Paragraph 35

-Subparagraph (f)

-URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62500-109447

+ Details

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

- Definition

Amount of (increase) decrease in standardized measure of discounted future net cash flow as a result of sales and transfers of oil and gas produced.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 235

-Section 50

-Paragraph 35

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62500-109447

+ Details

Name:	us-gaap_SalesAndTransfersOfOilAndGasProducedNetOfProductionCosts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of increase (decrease) in standardized measure of discounted future net cash flow as a result of changes from other sources.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 235

-Section 50

-Paragraph 35

-URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62500-109447

+ Details

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

- Details

Name:	dei_LegalEntityAxis=hnrg_SavoyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	hnrg_UnderlyingBasisAxis=hnrg_NymexStripPricesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	hnrg_UnderlyingBasisAxis=hnrg_SecAveragePricesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Equity Investment in Savoy (Carrying Value and Average Wellhead Prices) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Sep. 30, 2014
Reserve Quantities [Line Items]
Beginning of year	$ 90,800us-gaap_CrudeOilAndNaturalGasLiquids	$ 35,300us-gaap_CrudeOilAndNaturalGasLiquids
Sales, net of production costs	(11,000)	(12,600)
Net changes in prices and production costs	(5,700)	1,600
Extensions and discoveries	13,300	57,200
Revisions of previous quantity estimates	(61,000)	2,100
Change in production timing and other	3,100	3,700
Change in ownership from 45% to 40%	(4,500)
Accretion of discount	9,100us-gaap_AccretionOfDiscount	3,500us-gaap_AccretionOfDiscount
End of year	$ 34,100us-gaap_CrudeOilAndNaturalGasLiquids	$ 90,800us-gaap_CrudeOilAndNaturalGasLiquids
Savoy [Member]
Reserve Quantities [Line Items]
Equity method investment ownership percentage	40.00%		45.00%
NYMEX Strip Prices [Member] \| Oil [Member]
Reserve Quantities [Line Items]
Average wellhead prices	59
NYMEX Strip Prices [Member] \| Natural Gas Liquids [Member]
Reserve Quantities [Line Items]
Average wellhead prices	28
NYMEX Strip Prices [Member] \| Natural Gas [Member]
Reserve Quantities [Line Items]
Average wellhead prices	3.94
SEC Average Prices [Member] \| Oil [Member]
Reserve Quantities [Line Items]
Average wellhead prices	89	95
SEC Average Prices [Member] \| Natural Gas Liquids [Member]
Reserve Quantities [Line Items]
Average wellhead prices	41	42
SEC Average Prices [Member] \| Natural Gas [Member]
Reserve Quantities [Line Items]
Average wellhead prices	4.27	3.04