Document And Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2020	Mar. 03, 2021	Jun. 30, 2020
Document Information [Line Items]
Entity Central Index Key	0000353020
Entity Registrant Name	Aegion Corp
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Period Focus	FY
Document Fiscal Year Focus	2020
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Document Transition Report	false
Entity File Number	001-35328
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	45-3117900
Entity Address, Address Line One	17988 Edison Avenue
Entity Address, City or Town	Chesterfield
Entity Address, State or Province	MO
Entity Address, Postal Zip Code	63005-1195
City Area Code	636
Local Phone Number	530-8000
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Title of 12(b) Security	Class A Common Shares, $.01 par value
Trading Symbol	AEGN
Security Exchange Name	NASDAQ
Entity Public Float			$ 478,089,812
Entity Common Stock, Shares Outstanding		30,740,140