Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2020	Oct. 30, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Trading Symbol	CECE
Entity Registrant Name	CECO ENVIRONMENTAL CORP
Entity Central Index Key	0000003197
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Current Reporting Status	Yes
Entity File Number	0-07099
Entity Tax Identification Number	13-2566064
Entity Address, Address Line One	14651 North Dallas Parkway
Entity Address, Address Line Two	Suite 500
Entity Address, City or Town	Dallas
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	75254
City Area Code	214
Local Phone Number	357-6181
Entity Common Stock, Shares Outstanding		35,504,757
Entity Interactive Data Current	Yes
Entity Small Business	true
Entity Emerging Growth Company	false
Document Transition Report	false
Document Quarterly Report	true
Entity Shell Company	false
Title of 12(b) Security	Common Stock, par value $0.01 per share
Security Exchange Name	NASDAQ
Entity Incorporation, State or Country Code	DE