Note 2 - Accounting Policies - Investments in Variable Interest Entities (Details) - USD ($) $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2019		Sep. 30, 2018	[1]	Sep. 30, 2019		Sep. 30, 2018	[1]	Dec. 31, 2018
Current assets	$ 464,769				$ 464,769				$ 481,867
Current liabilities	233,497				233,497				219,650
Revenue	7,275		$ 16,405		20,719		$ 39,179
Gross profit	2,412		3,238		6,463		6,982
Net income attributable to Aegion Corporation	(2,154)		$ (946)		(2,773)		$ (886)
Variable Interest Entity, Primary Beneficiary [Member]
Current assets	18,236	[2]			18,236	[2]			33,066
Non-current assets	6,878	[2]			6,878	[2]			6,466
Current liabilities	8,949	[2]			8,949	[2]			12,953
Non-current liabilities	$ 3,252	[2]			$ 3,252	[2]			$ 8,780

[1] Includes activity from our pipe coating and insulation joint venture in Louisiana, which was sold during the third quarter of 2018.

[2] Includes $3.5 million of assets and $5.2 million of liabilities classified as held for sale related to United Mexico. See Note 5.