Note 12 - 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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net income attributable to Generac Holdings Inc.		$ 75,575	$ 75,776	$ 53,261	$ 33,645	$ 80,907	$ 39,435	$ 25,291	$ 12,175	$ 238,257	$ 157,808	$ 97,154
Redeemable noncontrolling interest redemption value adjustment										(17,970)	909	(909)
Net income attributable to common shareholders										$ 220,287	$ 158,717	$ 96,245
Weighted average shares, basic (in shares)										61,662,031	62,040,704	64,905,793
Dilutive effect of stock compensation awards (in shares)	[1]									571,194	602,168	476,981
Diluted shares (in shares)										62,233,225	62,642,872	65,382,774
Basic (in dollars per share)		$ 1.21	$ 1.12	$ 0.83	$ 0.42	$ 1.31	$ 0.64	$ 0.41	$ 0.21	$ 3.57	$ 2.56	$ 1.48
Diluted (in dollars per share)		$ 1.20	$ 1.11	$ 0.82	$ 0.42	$ 1.30	$ 0.63	$ 0.41	$ 0.20	$ 3.54	$ 2.53	$ 1.47

[1] Excludes approximately 26,100, 147,400 and 15,800 stock options for the years ended December 31, 2018, 2017 and 2016, respectively, as the impact of such awards was anti-dilutive.