Note 19 - Quarterly Financial Information (Unaudited) - Unaudited Quarterly Financial Information (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 sales	$ 1,067,071	$ 942,698	$ 919,981	$ 807,434	$ 761,082	$ 701,355	$ 546,848	$ 475,915	$ 3,737,184	$ 2,485,200	$ 2,204,336
Gross profit	362,539	335,994	339,735	321,814	300,202	276,149	208,983	172,320	1,360,082	957,654	797,752
Operating income	175,481	173,579	182,952	189,124	171,054	155,637	89,553	62,862	721,136	479,106	372,163
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
Net income attributable to common shareholders 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 common shareholders 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