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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
	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	$ 4,960invest_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	4,637invest_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	8,232invest_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		2,169invest_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			$ 3,472invest_DerivativeNotionalAmount / us-gaap_DerivativeInstrumentRiskAxis = gnrc_CommodityForwardContractFiveMember
Termination date			Sep. 30, 2013

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- Definition

Date the derivative contract become effective, in CCYY-MM-DD format.

+ References

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+ Details

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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

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- Definition

Date the entity entered into the derivative contract, in CCYY-MM-DD format.

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- Definition

Date the derivative contract matures, in CCYY-MM-DD format.

+ References

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