Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Cumulative Effect, Period of Adoption, Adjusted Balance [Member] Common Stock [Member]	Cumulative Effect, Period of Adoption, Adjusted Balance [Member] Additional Paid-in Capital [Member]	Cumulative Effect, Period of Adoption, Adjusted Balance [Member] Treasury Stock [Member]	Cumulative Effect, Period of Adoption, Adjusted Balance [Member] Excess Purchase Price over Predecessor Basis [Member]	Cumulative Effect, Period of Adoption, Adjusted Balance [Member] Retained Earnings [Member]	Cumulative Effect, Period of Adoption, Adjusted Balance [Member] AOCI Attributable to Parent [Member]	Cumulative Effect, Period of Adoption, Adjusted Balance [Member] Parent [Member]	Cumulative Effect, Period of Adoption, Adjusted Balance [Member] Noncontrolling Interest [Member]	Cumulative Effect, Period of Adoption, Adjusted Balance [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Excess Purchase Price over Predecessor Basis [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Parent [Member]	Noncontrolling Interest [Member]	Total
Balance (in shares) at Dec. 31, 2019										71,667,726		(9,103,013)
Balance at Dec. 31, 2019	$ 0	$ 0	$ 0	$ 0	$ (1,147)	$ 0	$ (1,147)	$ 0	$ (1,147)	$ 717	$ 498,866	$ (324,551)	$ (202,116)	$ 1,084,383	$ (24,917)	$ 1,032,382	$ 469	$ 1,032,851
Unrealized gain (loss) on interest rate swaps, net of tax										0	0	0	0	0	(18,406)	(18,406)	0	(18,406)
Foreign currency translation adjustment										$ 0	0	$ 0	0	0	(18,716)	(18,716)	(27)	(18,743)
Common stock issued under equity incentive plans, net of shares withheld for employee taxes and strike price (in shares)										344,176		0
Common stock issued under equity incentive plans, net of shares withheld for employee taxes and strike price										$ 3	5,417	$ 0	0	0	0	5,420	0	5,420
Net share settlement of restricted stock awards (in shares)										0		(67,721)
Net share settlement of restricted stock awards										$ 0	0	$ (6,962)	0	0	0	(6,962)	0	(6,962)
Share-based compensation										0	14,327	0	0	0	0	14,327	0	14,327
Redemption value adjustment										0	0	0	0	(2,281)	0	(2,281)	0	(2,281)
Net income attributable to Generac Holdings Inc.										$ 0	0	$ 0	0	225,575	0	225,575		225,575
Net income																	(738)
Net income																		224,837
Balance (in shares) at Sep. 30, 2020										72,011,902		(9,170,734)
Balance at Sep. 30, 2020										$ 720	518,610	$ (331,513)	(202,116)	1,306,530	(62,039)	1,230,192	(296)	1,229,896
Balance (in shares) at Jun. 30, 2020										71,960,067		(9,170,162)
Balance at Jun. 30, 2020										$ 720	512,318	$ (331,415)	(202,116)	1,190,749	(72,526)	1,097,730	(455)	1,097,275
Unrealized gain (loss) on interest rate swaps, net of tax															1,003	1,003		1,003
Foreign currency translation adjustment										$ 0	0	$ 0	0	0	9,484	9,484	(25)	9,459
Common stock issued under equity incentive plans, net of shares withheld for employee taxes and strike price (in shares)										51,835		0
Common stock issued under equity incentive plans, net of shares withheld for employee taxes and strike price										$ 0	1,939	$ 0	0	0	0	1,939	0	1,939
Net share settlement of restricted stock awards (in shares)										0		(572)
Net share settlement of restricted stock awards										$ 0	0	$ (98)	0	0	0	(98)	0	(98)
Share-based compensation										0	4,353	0	0	0	0	4,353	0	4,353
Redemption value adjustment										0	0	0	0	811	0	811	0	811
Net income attributable to Generac Holdings Inc.										$ 0	0	$ 0	0	114,970	0	114,970		114,970
Net income																	184
Net income																		115,154
Balance (in shares) at Sep. 30, 2020										72,011,902		(9,170,734)
Balance at Sep. 30, 2020										$ 720	518,610	$ (331,513)	(202,116)	1,306,530	(62,039)	1,230,192	(296)	1,229,896
Balance (in shares) at Dec. 31, 2020										72,024,329		(9,173,731)
Balance at Dec. 31, 2020										$ 721	525,541	$ (332,164)	(202,116)	1,432,565	(34,254)	1,390,293	(89)	1,390,204
Unrealized gain (loss) on interest rate swaps, net of tax															15,184	15,184		15,184
Foreign currency translation adjustment										$ 0	0	$ 0	0	0	(36,471)	(36,471)	(13)	(36,484)
Common stock issued under equity incentive plans, net of shares withheld for employee taxes and strike price (in shares)										280,736		0
Common stock issued under equity incentive plans, net of shares withheld for employee taxes and strike price										$ 3	7,417	$ 0	0	0	0	7,420	0	7,420
Common stock issued for business combination (in shares)										30,640		0
Common stock issued for business combination										$ 0	12,000	$ 0	0	0	0	12,000	0	12,000
Net share settlement of restricted stock awards (in shares)										0		(78,763)
Net share settlement of restricted stock awards										$ 0	0	$ (26,470)	0	0	0	(26,470)	0	(26,470)
Share-based compensation										0	18,204	0	0	0	0	18,204	0	18,204
Redemption value adjustment										0	0	0	0	(5,687)	0	(5,687)	0	(5,687)
Net income attributable to Generac Holdings Inc.										$ 0	0	$ 0	0	407,599	0	407,599		407,599
Net income																	307
Net income																		407,906
Balance (in shares) at Sep. 30, 2021										72,335,705		(9,252,494)
Balance at Sep. 30, 2021										$ 724	563,162	$ (358,634)	(202,116)	1,834,477	(55,541)	1,782,072	205	1,782,277
Balance (in shares) at Jun. 30, 2021										72,252,980		(9,252,097)
Balance at Jun. 30, 2021										$ 723	542,893	$ (358,481)	(202,116)	1,710,464	(37,583)	1,655,900	38	1,655,938
Unrealized gain (loss) on interest rate swaps, net of tax															2,941	2,941		2,941
Foreign currency translation adjustment															(20,899)	(20,899)	(8)	(20,907)
Common stock issued under equity incentive plans, net of shares withheld for employee taxes and strike price (in shares)										52,085
Common stock issued under equity incentive plans, net of shares withheld for employee taxes and strike price										$ 1	2,486					2,487		2,487
Common stock issued for business combination (in shares)										30,640
Common stock issued for business combination											12,000					12,000		12,000
Net share settlement of restricted stock awards (in shares)												(397)
Net share settlement of restricted stock awards												$ (153)				(153)		(153)
Share-based compensation										$ 0	5,783	0	0	0	0	5,783	0	5,783
Redemption value adjustment										0	0	0	0	(7,557)	0	(7,557)	0	(7,557)
Net income attributable to Generac Holdings Inc.										$ 0	0	$ 0	0	131,570	0	131,570		131,570
Net income																	175
Net income																		131,745
Balance (in shares) at Sep. 30, 2021										72,335,705		(9,252,494)
Balance at Sep. 30, 2021										$ 724	$ 563,162	$ (358,634)	$ (202,116)	$ 1,834,477	$ (55,541)	$ 1,782,072	$ 205	$ 1,782,277