Acquisition of Smile Energy G.K. (Details) - USD ($) $ / shares in Units, $ in Millions		9 Months Ended
Jun. 07, 2018	Sep. 30, 2018
Acquisition of Smile Energy G.K. (Textual)
Exercisable acquisition date	Jun. 07, 2020
Amortized straight-line basis over estimated life		10 years
Flower Power Service Agreement [Member]
Acquisition of Smile Energy G.K. (Textual)
Power service agreement fees		$ 0.4
Power service agreement initial term		3 years
Charging set-up fees to expense on a straight-line basis		3 years
Capital Sixty [Member]
Acquisition of Smile Energy G.K. (Textual)
Aggregate purchase price	$ 0.7
Purchase membership percentage	5.00%
Exercise price	$ 1
Genie Japan [Member]
Acquisition of Smile Energy G.K. (Textual)
Ownership interest percentage	100.00%
Option value	$ 0.3

Acquired agreement fees useful life.

No definition available.

Name:	gne_AcquiredAgreementFeesUsefulLife
Namespace Prefix:	gne_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Business combination consideration transferred other option cancellation payment amount.

+ References

No definition available.

+ Details

Name:	gne_BusinessCombinationConsiderationTransferredOtherOptionCancellationPaymentAmount
Namespace Prefix:	gne_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Date when the business acquisition agreement was exercisable, in CCYY-MM-DD format.

+ References

No definition available.

+ Details

Name:	gne_BusinessCombinationConsiderationTransferredOtherOptionExercisableDate
Namespace Prefix:	gne_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Business combination consideration transferred other option exercise price.

+ References

No definition available.

+ Details

Name:	gne_BusinessCombinationConsiderationTransferredOtherOptionExercisePrice
Namespace Prefix:	gne_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Business combination consideration transferred other option membership interest percentage.

+ References

No definition available.

+ Details

Name:	gne_BusinessCombinationConsiderationTransferredOtherOptionMembershipInterestPercentage
Namespace Prefix:	gne_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Term of agreement.

+ References

No definition available.

+ Details

Name:	gne_TermOfAgreement
Namespace Prefix:	gne_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16265-109275

+ Details

Name:	us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of voting equity interests acquired at the acquisition date in the business combination.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463

+ Details

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

- References

No definition available.

+ Details

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

- Definition

Amount of asset related to consideration paid in advance for other costs that provide economic benefits within a future period of one year or the normal operating cycle, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=82887183&loc=d3e6676-107765

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82887183&loc=d3e6787-107765

+ Details

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

- Definition

The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3213-108585

+ Details

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

- Details

Name:	gne_TypeOfAgreementAxis=gne_FlowerPowerServiceAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=gne_CapitalSixtyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=gne_GenieJapanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: