Note 12 - Segment and Geographic Information - Summary of Revenues (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
Revenues	[1]	$ 287,375	$ 276,904
Gross profit	[1]	49,884	48,295
Total operating income (loss)		1,396	(774)
Interest expense		(3,196)	(3,590)
Interest income		228	285
Other	[2]	425	(674)
Total other expense		(2,543)	(3,979)
Loss before taxes on income		(1,147)	(4,753)
UNITED STATES
Revenues	[1]	233,220	208,775
Gross profit	[1]	39,636	31,827
CANADA
Revenues	[1]	21,855	24,068
Gross profit	[1]	2,731	3,454
Europe [Member]
Revenues	[1]	10,671	16,003
Gross profit	[1]	2,948	3,519
Other Foreign Countries [Member]
Revenues	[1]	21,629	28,058
Gross profit	[1]	4,569	9,495
Infrastructure Solutions [Member]
Revenues		130,244	131,543
Infrastructure Solutions [Member] | UNITED STATES
Revenues		103,418	97,891
Infrastructure Solutions [Member] | CANADA
Revenues		11,023	10,611
Infrastructure Solutions [Member] | Europe [Member]
Revenues		7,642	12,525
Infrastructure Solutions [Member] | Other Foreign Countries [Member]
Revenues		8,161	10,516
Corrosion Protection [Member]
Revenues		66,068	64,498
Corrosion Protection [Member] | UNITED STATES
Revenues		38,739	30,021
Corrosion Protection [Member] | CANADA
Revenues		10,832	13,457
Corrosion Protection [Member] | Europe [Member]
Revenues		3,029	3,478
Corrosion Protection [Member] | Other Foreign Countries [Member]
Revenues		13,468	17,542
Energy Services [Member]
Revenues		91,063	80,863
Energy Services [Member] | UNITED STATES
Revenues		91,063	80,863
Energy Services [Member] | CANADA
Revenues		0	0
Energy Services [Member] | Europe [Member]
Revenues		0	0
Energy Services [Member] | Other Foreign Countries [Member]
Revenues		0	0
Operating Segments [Member] | Infrastructure Solutions [Member]
Revenues		130,244	131,543
Gross profit		31,370	26,586
Total operating income (loss)	[3]	13,555	5,715
Operating Segments [Member] | Corrosion Protection [Member]
Revenues		66,068	64,498
Gross profit		8,917	12,873
Total operating income (loss)	[4]	(6,447)	(1,760)
Operating Segments [Member] | Energy Services [Member]
Revenues		91,063	80,863
Gross profit		9,597	8,836
Total operating income (loss)		2,176	1,115
Corporate, Non-Segment [Member]
Total operating income (loss)	[5]	$ (7,888)	$ (5,844)

[1] Revenues and gross profit are attributed to the country of origin

[2] Other expense in the first quarters of 2020 and 2019 includes $0.6 million and $0.2 million of restructuring charges (see Note 4). Other expense in the first quarter of 2020 also includes gains of $0.4 million related to divestitures of Insituform Australia and Insituform Spain (see Note 1).

[3] Operating income in the first quarters of 2020 and 2019 includes $0.5 million and $2.1 million, respectively, of restructuring charges (see Note 4) and $0.2 million and $0.1 million, respectively, of costs primarily related to the divestiture of certain international operations.

[4] Operating loss in the first quarters of 2020 and 2019 includes $1.8 million and $0.2 million, respectively, of restructuring charges (see Note 4).

[5] Operating loss in the first quarters of 2020 and 2019 includes $0.7 million and $0.4 million, respectively, of restructuring charges (see Note 4). Operating loss in the first quarter of 2020 also includes $0.7 million of costs related to the divestiture of certain international operations.