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, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Earnings Per Share [Abstract]
Net loss attributable to CECO Environmental Corp.	$ 1,943	$ (1,249)	$ 9,122	$ 224
Denominator
Basic weighted-average shares outstanding	34,455,657	35,472,298	34,791,129	35,463,279
Common stock equivalents arising from stock options and restricted stock awards	415,000	0	244,000	267,000
Diluted weighted-average shares outstanding	34,871,313	35,472,298	35,035,041	35,729,887