Note 12 - Segment Reporting - Summary of Revenues (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenues	[1]	$ 275,884	$ 308,789	$ 808,276	$ 904,433
Gross profit	[1]	60,260	66,792	163,719	182,524
Total operating income (loss)		(27,240)	14,649	(17,117)	14,334
Interest expense		(4,288)	(3,446)	(12,174)	(10,602)
Interest income		258	268	701	814
Other	[2]	245	(5,236)	1,634	(6,925)
Total other expense		(3,785)	(8,414)	(9,839)	(16,713)
Income (loss) before taxes (benefit)		(31,025)	6,235	(26,956)	(2,379)
UNITED STATES
Revenues	[1]	212,407	231,904	643,074	680,666
Gross profit	[1]	44,808	48,331	125,778	130,950
CANADA
Revenues	[1]	34,325	32,124	81,175	89,584
Gross profit	[1]	7,003	6,424	15,103	14,906
Europe [Member]
Revenues	[1]	9,957	16,347	27,820	49,731
Gross profit	[1]	3,129	4,309	8,333	11,139
Other Foreign Countries [Member]
Revenues	[1]	19,195	28,414	56,207	84,452
Gross profit	[1]	5,320	7,728	14,505	25,529
Infrastructure Solutions [Member]
Revenues		152,102	156,087	419,738	443,069
Infrastructure Solutions [Member] | UNITED STATES
Revenues		119,334	112,357	337,457	321,205
Infrastructure Solutions [Member] | CANADA
Revenues		20,864	17,775	46,092	47,320
Infrastructure Solutions [Member] | Europe [Member]
Revenues		5,727	12,889	17,500	38,302
Infrastructure Solutions [Member] | Other Foreign Countries [Member]
Revenues		6,177	13,066	18,689	36,242
Corrosion Protection [Member]
Revenues		60,986	75,901	182,545	217,996
Corrosion Protection [Member] | UNITED STATES
Revenues		30,277	42,746	99,624	116,093
Corrosion Protection [Member] | CANADA
Revenues		13,461	14,349	35,083	42,264
Corrosion Protection [Member] | Europe [Member]
Revenues		4,230	3,458	10,320	11,429
Corrosion Protection [Member] | Other Foreign Countries [Member]
Revenues		13,018	15,348	37,518	48,210
Energy Services [Member]
Revenues		62,796	76,801	205,993	243,368
Energy Services [Member] | UNITED STATES
Revenues		62,796	76,801	205,993	243,368
Energy Services [Member] | CANADA
Revenues		0	0	0	0
Energy Services [Member] | Europe [Member]
Revenues		0	0	0	0
Energy Services [Member] | Other Foreign Countries [Member]
Revenues		0	0	0	0
Operating Segments [Member] | Infrastructure Solutions [Member]
Revenues		152,102	156,087	419,738	443,069
Gross profit		41,358	39,569	108,395	105,026
Total operating income (loss)	[3]	23,497	18,376	58,056	33,211
Operating Segments [Member] | Corrosion Protection [Member]
Revenues		60,986	75,901	182,545	217,996
Gross profit		13,432	17,232	36,460	46,797
Total operating income (loss)	[4]	(1,357)	2,362	(7,105)	(3,261)
Operating Segments [Member] | Energy Services [Member]
Revenues		62,796	76,801	205,993	243,368
Gross profit		5,470	9,991	18,864	30,701
Total operating income (loss)	[5]	(41,701)	2,257	(45,238)	7,479
Corporate, Non-Segment [Member]
Total operating income (loss)	[6]	$ (7,679)	$ (8,346)	$ (22,830)	$ (23,095)

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

[2] Other income in the third quarter of 2020 includes gains of $1.5 million related to restructuring (see Note 4) and a $0.6 million loss on the sale of Insituform Australia (see Note 1). Other expense in the third quarter of 2019 includes $5.3 million of restructuring charges (see Note 4). Other income (expense) in the first nine months of 2020 and 2019 includes gains of $1.8 million and charges of $6.5 million, respectively, related to restructuring (see Note 4). Other income in the first nine months of 2020 also includes gains of $0.1 million related to divestitures of Insituform Australia and Insituform Spain (see Note 1).

[3] Operating income in the third quarters of 2020 and 2019 includes reversals of $0.2 million and charges of $1.2 million, respectively, related to restructuring (see Note 4). Additionally, the third quarter of 2019 includes $0.5 million of costs primarily related to the divestiture of certain international operations. Operating income in the first nine months of 2020 and 2019 includes $0.4 million and $4.7 million, respectively, of restructuring charges (see Note 4) and $0.2 million and $1.0 million, respectively, of divestiture costs. Additionally, operating income in the first nine months of 2020 includes $0.7 million of impairment reversals while operating income in the first nine months of 2019 includes $9.0 million of impairment charges to assets held for sale.

[4] Operating income (loss) in the third quarters of 2020 and 2019 includes $4.5 million and $0.8 million, respectively, of restructuring charges (see Note 4). Operating loss in the first nine months of 2020 and 2019 includes $7.6 million and $4.3 million, respectively, of restructuring charges (see Note 4). Additionally, operating loss in the first nine months of 2019 includes $2.9 million of impairment charges to assets held for sale.

[5] Operating income (loss) in the third quarters of 2020 and 2019 includes $0.9 million and $0.1 million, respectively, of restructuring charges (see Note 4). Additionally, operating loss in the third quarter of 2020 includes goodwill impairment charges of $39.4 million. Operating income (loss) in the first nine months of 2020 and 2019 includes $2.2 million and $0.2 million, respectively, of restructuring charges (see Note 4). Additionally, operating loss in the first nine months of 2020 includes $40.7 million of goodwill impairment charges and $1.0 million of definite-lived intangible asset impairment charges.

[6] Operating loss in the third quarters of 2020 and 2019 includes $0.5 million and $1.1 million, respectively, of restructuring charges (see Note 4) and $0.7 million and $1.3 million, respectively, of divestiture costs. Operating loss in the first nine months of 2020 and 2019 includes $2.0 million and $2.4 million, respectively, of restructuring charges (see Note 4) and $2.0 million and $1.6 million, respectively, of divestiture costs.