Note 17 - Subsequent Events (Details Textual) - USD ($) $ in Millions			3 Months Ended		12 Months Ended
	Feb. 13, 2020	Jan. 24, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2019
Insituform Pacific Pty Limited ("IPPL") [Member] | Discontinued Operations, Disposed of by Sale [Member]
Disposal Group, Not Discontinued Operation, Loss (Gain) on Write-down				$ 5.1
Insituform Spain [Member] | Discontinued Operations, Disposed of by Sale [Member]
Disposal Group, Not Discontinued Operation, Loss (Gain) on Write-down			$ 6.0
Trademarks [Member]
Finite-Lived Intangible Asset, Useful Life					8 years 3 months 18 days
Insituform Pacific Pty Limited ("IPPL") [Member] | Subsequent Event [Member]
Tube-Supply Agreement, Term		5 years
Insituform Pacific Pty Limited ("IPPL") [Member] | Subsequent Event [Member] | Trademarks [Member]
Finite-Lived Intangible Asset, Useful Life		5 years
Insituform Spain [Member] | Subsequent Event [Member]
Tube-Supply Agreement, Term	5 years
Insituform Spain [Member] | Subsequent Event [Member] | Trademarks [Member]
Finite-Lived Intangible Asset, Useful Life	5 years