Note 17 - Quarterly Financial Information (Unaudited) - Unaudited Quarterly Financial Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net sales	$ 417,421	$ 373,121	$ 367,376	$ 286,535	$ 357,830	$ 359,291	$ 288,360	$ 311,818	$ 1,444,453	$ 1,317,299	$ 1,460,919
Gross profit	154,127	137,772	124,147	98,060	131,124	130,326	95,897	102,603	514,106	459,950	516,219
Operating income	77,231	56,340	44,082	26,964	27,316	67,867	39,467	44,911	204,617	179,561	293,375
Net income attributable to Generac Holdings Inc.	$ 41,509	$ 26,183	$ 20,888	$ 10,208	$ 9,182	$ 34,036	$ 14,844	$ 19,685	$ 98,788	$ 77,747	$ 174,613
Net income attributable to common shareholders per common share - basic: (in dollars per share)	$ 0.64	$ 0.41	$ 0.32	$ 0.15	$ 0.14	$ 0.50	$ 0.22	$ 0.29	$ 1.51	$ 1.14	$ 2.55
Net income attributable to common shareholders per common share - diluted: (in dollars per share)	$ 0.64	$ 0.40	$ 0.31	$ 0.15	$ 0.14	$ 0.49	$ 0.21	$ 0.28	$ 1.50	$ 1.12	$ 2.49