Note 5 - Assets and Liabilities Held for Sale (Details Textual) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Impairment of Long-Lived Assets to be Disposed of	$ 0	$ 11,900	$ 0	$ 11,946	$ 0
Infrastructure Solutions [Member]
Impairment of Long-Lived Assets to be Disposed of				9,000
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		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