Note 6 - Assets and Liabilities Held for Sale (Details Textual) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Impairment of Long-Lived Assets to be Disposed of			$ 23,427	$ 0	$ 0
Corporate, Non-Segment [Member]
Impairment of Long-Lived Assets to be Disposed of	$ 2,900		2,900
Infrastructure Solutions [Member]
Impairment of Long-Lived Assets to be Disposed of			17,600
Corrosion Protection [Member]
Impairment of Long-Lived Assets to be Disposed of			$ 2,900
Insituform Australia [Member] | Infrastructure Solutions [Member]
Impairment of Long-Lived Assets to be Disposed of		$ 5,100
Insituform Netherlands [Member] | Infrastructure Solutions [Member]
Impairment of Long-Lived Assets to be Disposed of	2,600	3,900
Corrpower [Member] | Corrosion Protection [Member]
Impairment of Long-Lived Assets to be Disposed of		1,100
United Mexico [Member] | Corrosion Protection [Member]
Impairment of Long-Lived Assets to be Disposed of		$ 1,800
Insituform Spain [Member] | Infrastructure Solutions [Member]
Impairment of Long-Lived Assets to be Disposed of	$ 6,000