Note 12 - Segment Reporting - Summary of Revenues (Details) - USD ($)		3 Months Ended				6 Months Ended
		Jun. 30, 2019		Jun. 30, 2018		Jun. 30, 2019		Jun. 30, 2018
Revenues	[1]	$ 318,740,000		$ 335,030,000		$ 595,644,000		$ 659,891,000
Gross profit	[1]	67,437,000		71,053,000		115,732,000		132,557,000
Total operating income (loss)		459,000		14,459,000		(315,000)		17,640,000
Interest expense		(3,566,000)		(3,923,000)		(7,156,000)		(9,366,000)
Interest income		261,000		62,000		546,000		109,000
Other	[2]	(1,015,000)		(506,000)		(1,689,000)		(768,000)
Total other expense		(4,320,000)		(4,367,000)		(8,299,000)		(10,025,000)
Income (loss) before taxes on income		(3,861,000)		10,092,000		(8,614,000)		7,615,000
UNITED STATES
Revenues		239,987,000	[1]	253,699,000	[1]	448,762,000	[3]	490,231,000	[1]
Gross profit	[1]	50,792,000		58,599,000		82,619,000		108,162,000
CANADA
Revenues	[1]	33,392,000		30,426,000		57,460,000		59,265,000
Gross profit	[1]	5,028,000		5,454,000		8,482,000		10,229,000
Europe [Member]
Revenues	[1]	17,381,000		15,846,000		33,384,000		31,855,000
Gross profit	[1]	3,311,000		1,401,000		6,830,000		2,535,000
Other Foreign Countries [Member]
Revenues	[1]	27,980,000		35,059,000		56,038,000		78,540,000
Gross profit	[1]	8,306,000		5,599,000		17,801,000		11,631,000
Infrastructure Solutions [Member]
Revenues		155,440,000		160,732,000		286,983,000		295,159,000
Infrastructure Solutions [Member] | UNITED STATES
Revenues		110,957,000		117,580,000		208,848,000		211,425,000
Infrastructure Solutions [Member] | CANADA
Revenues		18,934,000		15,607,000		29,545,000		27,876,000
Infrastructure Solutions [Member] | Europe [Member]
Revenues		12,888,000		12,996,000		25,413,000		26,140,000
Infrastructure Solutions [Member] | Other Foreign Countries [Member]
Revenues		12,661,000		14,549,000		23,177,000		29,718,000
Corrosion Protection [Member]
Revenues		77,596,000		96,389,000		142,094,000		194,494,000
Corrosion Protection [Member] | UNITED STATES
Revenues		43,326,000		58,210,000		73,347,000		108,568,000
Corrosion Protection [Member] | CANADA
Revenues		14,458,000		14,819,000		27,915,000		31,389,000
Corrosion Protection [Member] | Europe [Member]
Revenues		4,493,000		2,850,000		7,971,000		5,715,000
Corrosion Protection [Member] | Other Foreign Countries [Member]
Revenues		15,319,000		20,510,000		32,861,000		48,822,000
Energy Services [Member]
Revenues		85,704,000		77,909,000		166,567,000		170,238,000
Energy Services [Member] | UNITED STATES
Revenues		85,704,000		77,909,000		166,567,000		170,238,000
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		155,439,000		160,732,000		286,982,000		295,159,000
Gross profit		38,871,000		35,949,000		65,458,000		62,658,000
Total operating income (loss)	[3]	9,120,000		12,916,000		14,835,000		16,153,000
Operating Segments [Member] | Corrosion Protection [Member]
Revenues		77,597,000		96,389,000		142,095,000		194,494,000
Gross profit		16,692,000		24,537,000		29,564,000		48,113,000
Total operating income (loss)	[4]	(3,863,000)		6,953,000		(5,623,000)		11,915,000
Operating Segments [Member] | Energy Services [Member]
Revenues		85,704,000		77,909,000		166,567,000		170,238,000
Gross profit		11,874,000		10,567,000		20,710,000		21,786,000
Total operating income (loss)		4,107,000		2,498,000		5,222,000		5,625,000
Corporate, Non-Segment [Member]
Total operating income (loss)	[5]	$ (8,905,000)		$ (7,908,000)		$ (14,749,000)		$ (16,053,000)

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

[2] Other expense in the second quarter and first six months of 2019 includes $0.9 million and $1.1 million, respectively, of 2017 Restructuring charges (see Note 4).

[3] Operating income in the second quarter of 2019 and 2018 includes $1.4 million and $2.5 million, respectively, of 2017 Restructuring charges and $0.4 million and $0.2 million, respectively, of costs primarily related to the planned divestiture of certain international operations (see note 4). Operating income in the first six months of 2019 and 2018 includes $3.4 million and $5.7 million, respectively, of 2017 Restructuring charges and $0.5 million and $0.2 million, respectively, of divestiture costs. Additionally, operating income in the second quarter and first six months of 2019 includes $9.0 million of impairment charges to assets held for sale (see Note 5).

[4] Operating income (loss) in the second quarter of 2019 and 2018 includes $3.3 million and $0.3 million, respectively, of 2017 Restructuring charges and less than $0.1 million and $0.1 million, respectively, of costs primarily related to the planned divestiture of certain international operations (see Note 4). Operating income (loss) in the first six months of 2019 and 2018 includes $3.5 million and $1.8 million, respectively, of 2017 restructuring charges, and less than $0.1 million and $0.2 million, respectively, of costs primarily related to the planned divestiture of certain international operations. Additionally, operating income in the second quarter and first six months of 2019 includes $2.9 million of impairment charges to assets held for sale (see Note 5).

[5] Operating loss in the second quarter of 2019 and 2018 includes $0.9 and less than $0.1 million, respectively, of 2017 Restructuring charges, and $0.4 million and $0.5 million, respectively of costs primarily related to the planned divestiture of certain international operations (see Note 4). Operating loss in the first six months of 2019 and 2018 includes $1.3 million and $0.6 million, respectively, of 2017 Restructuring charges and $0.4 million and $0.8 million, respectively of divestiture costs.