Note 3 - Revenue - Disaggregation of Revenue (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
Fixed-price Contract [Member]
Revenues		190,558,000		219,481,000		352,965,000		428,401,000
Time-and-materials Contract [Member]
Revenues		101,696,000		93,383,000		196,616,000		193,063,000
Product Sales [Member]
Revenues		26,442,000		22,153,000		45,869,000		38,394,000
License Fees [Member]
Revenues		44,000		13,000		194,000		33,000
Infrastructure Solutions [Member]
Revenues		155,440,000		160,732,000		286,983,000		295,159,000
Infrastructure Solutions [Member] | Fixed-price Contract [Member]
Revenues		136,212,000		149,532,000		255,127,000		274,794,000
Infrastructure Solutions [Member] | Time-and-materials Contract [Member]
Revenues		0		0		0		0
Infrastructure Solutions [Member] | Product Sales [Member]
Revenues		19,184,000		11,187,000		31,662,000		20,332,000
Infrastructure Solutions [Member] | License Fees [Member]
Revenues		44,000		13,000		194,000		33,000
Corrosion Protection [Member]
Revenues		77,596,000		96,389,000		142,094,000		194,494,000
Corrosion Protection [Member] | Fixed-price Contract [Member]
Revenues		53,055,000		63,982,000		95,628,000		141,883,000
Corrosion Protection [Member] | Time-and-materials Contract [Member]
Revenues		17,283,000		21,441,000		32,259,000		34,549,000
Corrosion Protection [Member] | Product Sales [Member]
Revenues		7,258,000		10,966,000		14,207,000		18,062,000
Corrosion Protection [Member] | License Fees [Member]
Revenues		0		0		0		0
Energy Services [Member]
Revenues		85,704,000		77,909,000		166,567,000		170,238,000
Energy Services [Member] | Fixed-price Contract [Member]
Revenues		1,291,000		5,967,000		2,210,000		11,724,000
Energy Services [Member] | Time-and-materials Contract [Member]
Revenues		84,413,000		71,942,000		164,357,000		158,514,000
Energy Services [Member] | Product Sales [Member]
Revenues		0		0		0		0
Energy Services [Member] | License Fees [Member]
Revenues		0		0		0		0
UNITED STATES
Revenues		239,987,000	[1]	253,699,000	[1]	448,762,000	[2]	490,231,000	[1]
UNITED STATES | Infrastructure Solutions [Member]
Revenues		110,957,000		117,580,000		208,848,000		211,425,000
UNITED STATES | Corrosion Protection [Member]
Revenues		43,326,000		58,210,000		73,347,000		108,568,000
UNITED STATES | Energy Services [Member]
Revenues		85,704,000		77,909,000		166,567,000		170,238,000
CANADA
Revenues	[1]	33,392,000		30,426,000		57,460,000		59,265,000
CANADA | Infrastructure Solutions [Member]
Revenues		18,934,000		15,607,000		29,545,000		27,876,000
CANADA | Corrosion Protection [Member]
Revenues		14,458,000		14,819,000		27,915,000		31,389,000
CANADA | Energy Services [Member]
Revenues		0		0		0		0
Europe [Member]
Revenues	[1]	17,381,000		15,846,000		33,384,000		31,855,000
Europe [Member] | Infrastructure Solutions [Member]
Revenues		12,888,000		12,996,000		25,413,000		26,140,000
Europe [Member] | Corrosion Protection [Member]
Revenues		4,493,000		2,850,000		7,971,000		5,715,000
Europe [Member] | Energy Services [Member]
Revenues		0		0		0		0
Other Foreign Countries [Member]
Revenues	[1]	27,980,000		35,059,000		56,038,000		78,540,000
Other Foreign Countries [Member] | Infrastructure Solutions [Member]
Revenues		12,661,000		14,549,000		23,177,000		29,718,000
Other Foreign Countries [Member] | Corrosion Protection [Member]
Revenues		15,319,000		20,510,000		32,861,000		48,822,000
Other Foreign Countries [Member] | Energy Services [Member]
Revenues		$ 0		$ 0		$ 0		$ 0

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

[2] 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).