Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Feb. 25, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Entity Registrant Name	CECO ENVIRONMENTAL CORP.
Trading Symbol	CECE
Entity Central Index Key	0000003197
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Interactive Data Current	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Well Known Seasoned Issuer	No
Entity Public Float			$ 166.2
Entity Common Stock Shares Outstanding		35,350,727
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	false
Title of 12(b) Security	Common Stock, par value $0.01 per share
Security Exchange Name	NASDAQ
Entity File Number	0-7099
Entity Incorporation, State or Country Code	DE
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
Document Annual Report	true
Document Transition Report	false
ICFR Auditor Attestation Flag	true
Documents Incorporated by Reference [Text Block]	Portions of the definitive Proxy Statement for the 2021 Annual Meeting of Stockholders, which is to be filed with the Securities and Exchange Commission within 120 days of the fiscal year ended December 31, 2020, are incorporated by reference into Part III of this Annual Report to the extent described herein.