Acquisition - Schedule of Unaudited Pro Forma Financial Information (Details) - Environmental Integrated Solutionsn and Mader Holdings L.P. [Member] - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Business Acquisition [Line Items]
Net Sales	$ 77,943	$ 91,099	$ 246,550	$ 269,982
Net (loss) income attributable to CECO Environmental Corp.	$ (222)	$ 2,468	$ 7,975	$ 10,788
(Loss) earnings per share:
Basic	$ (0.01)	$ 0.07	$ 0.23	$ 0.31
Diluted	$ (0.01)	$ 0.07	$ 0.22	$ 0.30