Note 14 - Earnings Per Share - Reconciliation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Net income attributable to Generac Holdings Inc.		$ 142,895	$ 131,570	$ 127,036	$ 148,993	$ 125,001	$ 114,970	$ 66,145	$ 44,460	$ 550,494	$ 350,576	$ 252,007
Redeemable noncontrolling interest redemption value adjustment										(17,102)	(1,247)	1,253
Net income attributable to common shareholders										$ 533,392	$ 349,329	$ 253,260
Weighted average shares, basic (in shares)										62,686,001	62,280,889	61,926,986
Dilutive effect of stock compensation awards (in shares)	[1]									1,534,603	1,456,845	938,460
Dilutive effect of contingently issued shares (in shares)										32,804	0	0
Diluted shares (in shares)										64,253,408	63,737,734	62,865,446
Net income attributable to Generac Holdings Inc. per common share - basic: (in dollars per share)		$ 2.09	$ 1.98	$ 2.06	$ 2.39	$ 2.02	$ 1.86	$ 1.04	$ 0.69	$ 8.51	$ 5.61	$ 4.09
Net income attributable to Generac Holdings Inc. per common share - diluted: (in dollars per share)		$ 2.04	$ 1.93	$ 2.01	$ 2.33	$ 1.96	$ 1.82	$ 1.02	$ 0.68	$ 8.30	$ 5.48	$ 4.03

[1] There were no awards with an anti-dilutive impact for the years ended December 31, 2021, 2020 and 2019.