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Note 4 - Derivative Instruments and Hedging Activities (Details) - Outstanding Commodity Forward Contracts (USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Commodity Forward Contract One [Member] |  |  |
Note 4 - Derivative Instruments and Hedging Activities (Details) - Outstanding Commodity Forward Contracts [Line Items] |  |  |
Trade date | Oct. 02, 2014 |  |
Effective date | Oct. 01, 2014 |  |
Notional amount | $ 4,960 invest_DerivativeNotionalAmount / us-gaap_DerivativeInstrumentRiskAxis = gnrc_CommodityForwardContractOneMember |  |
Termination date | Dec. 31, 2015 |  |
Commodity Forward Contract Two [Member] |  |  |
Note 4 - Derivative Instruments and Hedging Activities (Details) - Outstanding Commodity Forward Contracts [Line Items] |  |  |
Trade date | Oct. 15, 2014 |  |
Effective date | Nov. 01, 2014 |  |
Notional amount | 4,637 invest_DerivativeNotionalAmount / us-gaap_DerivativeInstrumentRiskAxis = gnrc_CommodityForwardContractTwoMember |  |
Termination date | Dec. 31, 2015 |  |
Commodity Forward Contract Three [Member] |  |  |
Note 4 - Derivative Instruments and Hedging Activities (Details) - Outstanding Commodity Forward Contracts [Line Items] |  |  |
Trade date | Dec. 01, 2014 |  |
Effective date | Dec. 01, 2014 |  |
Notional amount | 8,232 invest_DerivativeNotionalAmount / us-gaap_DerivativeInstrumentRiskAxis = gnrc_CommodityForwardContractThreeMember |  |
Termination date | Dec. 31, 2015 |  |
Commodity Forward Contract Four [Member] |  |  |
Note 4 - Derivative Instruments and Hedging Activities (Details) - Outstanding Commodity Forward Contracts [Line Items] |  |  |
Trade date |  | Jun. 21, 2013 |
Effective date |  | Oct. 01, 2013 |
Notional amount |  | 2,169 invest_DerivativeNotionalAmount / us-gaap_DerivativeInstrumentRiskAxis = gnrc_CommodityForwardContractFourMember |
Termination date |  | Jun. 30, 2014 |
Commodity Forward Contract Five [Member] |  |  |
Note 4 - Derivative Instruments and Hedging Activities (Details) - Outstanding Commodity Forward Contracts [Line Items] |  |  |
Trade date |  |  | Oct. 29, 2012
Effective date |  |  | Jan. 01, 2013
Notional amount |  |  | $ 3,472 invest_DerivativeNotionalAmount / us-gaap_DerivativeInstrumentRiskAxis = gnrc_CommodityForwardContractFiveMember
Termination date |  |  | Sep. 30, 2013

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- Definition Aggregate notional amount specified by the derivative(s). Expressed as an absolute value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
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