Note 16 - Subsequent Event	12 Months Ended
Dec. 31, 2020
Notes to Financial Statements
Subsequent Events [Text Block]	16. SUBSEQUENT EVENT On February 16, 2021, the Company entered into a definitive merger agreement with affiliates of New Mountain Capital, L.L.C., a leading growth-oriented investment firm headquartered in New York. The transaction is valued at approximately $963 million, or $26.00 per common share, and was unanimously approved by the Company’s board of directors. Upon completion of the transaction, Aegion will become a private company and shares of Aegion common stock will no longer be listed on any public market. The merger is expected to close in the second quarter of 2021, subject to customary closing conditions, including, among other things, approval under the HSR Act and approval of the Company’s stockholders. In connection with the merger, any unvested restricted stock units and performance stock units will become fully vested at the time of the completed transaction and convert into the right to receive a cash payment equal to the per share transaction valuation. This conversion could be material. The merger agreement also includes customary termination provisions for both parties, subject, in certain circumstances, to the payment by the Company of a termination fee of $30,000,000. As a result of the agreement, the Company terminated the open market share repurchase program effective February 16, 2021. For the period January 1, 2021 through February 15, 2021, the Company acquired 39,501 shares of the Company’s common stock for $0.8 million ($19.84 average price per share).

Note 16 - Subsequent Event

12 Months Ended

Dec. 31, 2020

16. SUBSEQUENT EVENT

On February 16, 2021, the Company entered into a definitive merger agreement with affiliates of New Mountain Capital, L.L.C., a leading growth-oriented investment firm headquartered in New York. The transaction is valued at approximately $963 million, or $26.00 per common share, and was unanimously approved by the Company’s board of directors. Upon completion of the transaction, Aegion will become a private company and shares of Aegion common stock will no longer be listed on any public market. The merger is expected to close in the second quarter of 2021, subject to customary closing conditions, including, among other things, approval under the HSR Act and approval of the Company’s stockholders. In connection with the merger, any unvested restricted stock units and performance stock units will become fully vested at the time of the completed transaction and convert into the right to receive a cash payment equal to the per share transaction valuation. This conversion could be material. The merger agreement also includes customary termination provisions for both parties, subject, in certain circumstances, to the payment by the Company of a termination fee of $30,000,000.

As a result of the agreement, the Company terminated the open market share repurchase program effective February 16, 2021. For the period January 1, 2021 through February 15, 2021, the Company acquired 39,501 shares of the Company’s common stock for $0.8 million ($19.84 average price per share).