Earnings per Share - Number of Shares Outstanding for Calculation of Earnings Per Share (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Earnings Per Share [Abstract]
Net loss attributable to CECO Environmental Corp.	$ 3,330	$ 1,943	$ 9,032	$ 9,122
Denominator
Basic weighted-average shares outstanding	34,771,742	34,455,657	34,612,163	34,791,129
Common stock equivalents arising from stock options and restricted stock awards	529,000	415,000	604,000	244,000
Diluted weighted-average shares outstanding	35,301,429	34,871,313	35,215,843	35,035,041