Note 2 - Accounting Policies - Investments in Variable Interest Entities (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Current assets		$ 434,980		$ 434,980		$ 450,215
Current liabilities		222,090		222,090		234,041
Revenue	[1]	275,884	$ 308,789	808,276	$ 904,433
Gross profit	[1]	60,260	66,792	163,719	182,524
Net income (loss) attributable to Aegion Corporation		(28,474)	6,036	(26,250)	(6,331)
Variable Interest Entity, Primary Beneficiary [Member]
Current assets		21,057		21,057		18,304
Non-current assets		7,764		7,764		7,635
Current liabilities		9,721		9,721		8,261
Non-current liabilities		1,557		1,557		$ 1,962
Revenue		8,677	7,275	22,132	20,719
Gross profit		3,354	2,412	7,735	6,463
Net income (loss) attributable to Aegion Corporation		$ 534	$ (2,154)	$ 889	$ (2,773)

[1] Revenues and gross profit are attributed to the country of origin