Note 5 - Assets and Liabilities Held for Sale - Assets and Liabilities Held for Sale (Details) - USD ($) $ in Thousands	9 Months Ended			12 Months Ended
	Sep. 30, 2020		Sep. 30, 2019	Dec. 31, 2019
Disposal Group, Including Discontinued Operation, Contract Assets, Current	$ 900			$ 5,400
Total current assets	11,083			16,092
Impairment of assets held for sale	0		$ (11,946)
Disposal Group, Including Discontinued Operation, Contract Liabilities, Current	100			100
Total current liabilities	1,864			6,485
Disposal Group, Held-for-sale, Not Discontinued Operations [Member]
Receivables, net	423	[1]		4,136	[2]
Retainage	483	[1]		518	[2]
Disposal Group, Including Discontinued Operation, Contract Assets, Current	882	[1]		5,350	[2]
Inventories	123	[1]		2,097	[2]
Prepaid expenses and other current assets	261	[1]		799	[2]
Total current assets	2,172	[1]		12,900	[2]
Property, plant & equipment, less accumulated depreciation	7,357	[1]		10,962	[2]
Goodwill	2,640	[1]		4,224	[2]
Intangible assets, less accumulated amortization	1,492	[1]		1,528	[2]
Operating lease assets	156	[1]		326	[2]
Other non-current assets	127	[1]		130	[2]
Impairment of assets held for sale	(2,861)	[1]		(13,978)	[2]
Total assets held for sale	11,083	[1]		16,092	[2]
Accounts payable	362	[1]		2,174	[2]
Accrued expenses	1,306	[1]		3,961	[2]
Disposal Group, Including Discontinued Operation, Contract Liabilities, Current	44	[1]		122	[2]
Total current liabilities	1,712	[1]		6,257	[2]
Operating lease liabilities	97	[1]		174	[2]
Other non-current liabilities	55	[1]		54	[2]
Total liabilities held for sale	$ 1,864	[1]		$ 6,485	[2]

[1] Includes Environmental Techniques and land held at Corporate.

[2] Includes Insituform Australia, Insituform Spain, Environmental Techniques and land held at Corporate.