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Legal and Regulatory Proceedings (Details) - USD ($) $ in Millions |  | 12 Months Ended
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Feb. 23, 2016 | Dec. 31, 2015
Legal Proceedings (Textual) |  |
Aggregate amount accrued for complaints and lawsuits |  | $ 2.5
Proposed regulatory matter potential requirements customer data, Description |  | As of December 31, 2015, New York represented 53% of GRE's total meters served and 44% of the total RCEs of GRE's customer base.
Subsequent Event [Member] |  |
Legal Proceedings (Textual) |  |
Proposed regulatory matter potential requirements, Description | The PSC's order, which was to become effective March 4, 2016, would require that all REPs' electricity and natural gas offerings to residential and small business customers include an annual guarantee of savings compared to the price charged by the relevant incumbent utility or, for electricity offerings, provide at least 30% of the supply from renewable sources. |

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- Definition Amount of loss contingency liability expected to be resolved within one year or the normal operating cycle, if longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349 + Details
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