Earnings per Share - Number of Shares Outstanding for Calculation of Earnings Per Share (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Earnings Per Share [Abstract]
Net loss attributable to CECO Environmental Corp.	$ 2,792	$ 1,181
Denominator
Basic weighted-average shares outstanding	35,051,034	35,396,705
Common stock equivalents arising from stock options and restricted stock awards	148,000	377,000
Diluted weighted-average shares outstanding	35,199,201	35,774,208