Number of shares that have been repurchased during the period and are being held in treasury

No definition available.

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Namespace Prefix:	gnrc_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash outflow to reacquire common stock during the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3291-108585

+ Details

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

- Definition

Amount of stock repurchase plan authorized.

+ References

No definition available.

+ Details

Name:	us-gaap_StockRepurchaseProgramAuthorizedAmount1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Period which shares may be purchased under a stock repurchase plan authorized by an entity's Board of Directors, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_StockRepurchaseProgramPeriodInForce1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Total cost of shares repurchased divided by the total number of shares repurchased.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6405813&loc=d3e23239-112655

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_StatementEquityComponentsAxis=us-gaap_TreasuryStockMember
Namespace Prefix:
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Balance Type:
Period Type:

Note 13 - Stock Repurchase Program (Details Textual) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended			53 Months Ended
	Sep. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Oct. 31, 2016	Aug. 31, 2015
Stock Repurchase Program, Authorized Amount	$ 250,000					$ 250,000	$ 200,000
Stock Repurchase Program, Period in Force	24 months
Payments for Repurchase of Common Stock		$ (0)	$ 25,656	$ 30,012	$ 305,547
Treasury Stock Acquired, Average Cost Per Share					$ 35.21
Treasury Stock [Member]
Shares Acquired Under Stock Repurchases Program, Shares		0	560,000	844,500	8,676,706