Note 3 - Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
Revenues	[1]	$ 287,375	$ 276,904
Fixed-price Contract [Member]
Revenues		158,496	162,406
Time-and-materials Contract [Member]
Revenues		102,303	94,921
Product Sales [Member]
Revenues		26,576	19,427
License Fees [Member]
Revenues		0	150
Infrastructure Solutions [Member]
Revenues		130,244	131,543
Infrastructure Solutions [Member] | Fixed-price Contract [Member]
Revenues		112,511	118,915
Infrastructure Solutions [Member] | Time-and-materials Contract [Member]
Revenues		0	0
Infrastructure Solutions [Member] | Product Sales [Member]
Revenues		17,733	12,478
Infrastructure Solutions [Member] | License Fees [Member]
Revenues		0	150
Corrosion Protection [Member]
Revenues		66,068	64,498
Corrosion Protection [Member] | Fixed-price Contract [Member]
Revenues		44,255	42,572
Corrosion Protection [Member] | Time-and-materials Contract [Member]
Revenues		12,970	14,977
Corrosion Protection [Member] | Product Sales [Member]
Revenues		8,843	6,949
Corrosion Protection [Member] | License Fees [Member]
Revenues		0	0
Energy Services [Member]
Revenues		91,063	80,863
Energy Services [Member] | Fixed-price Contract [Member]
Revenues		1,730	919
Energy Services [Member] | Time-and-materials Contract [Member]
Revenues		89,333	79,944
Energy Services [Member] | Product Sales [Member]
Revenues		0	0
Energy Services [Member] | License Fees [Member]
Revenues		0	0
UNITED STATES
Revenues	[1]	233,220	208,775
UNITED STATES | Infrastructure Solutions [Member]
Revenues		103,418	97,891
UNITED STATES | Corrosion Protection [Member]
Revenues		38,739	30,021
UNITED STATES | Energy Services [Member]
Revenues		91,063	80,863
CANADA
Revenues	[1]	21,855	24,068
CANADA | Infrastructure Solutions [Member]
Revenues		11,023	10,611
CANADA | Corrosion Protection [Member]
Revenues		10,832	13,457
CANADA | Energy Services [Member]
Revenues		0	0
Europe [Member]
Revenues	[1]	10,671	16,003
Europe [Member] | Infrastructure Solutions [Member]
Revenues		7,642	12,525
Europe [Member] | Corrosion Protection [Member]
Revenues		3,029	3,478
Europe [Member] | Energy Services [Member]
Revenues		0	0
Other Foreign Countries [Member]
Revenues	[1]	21,629	28,058
Other Foreign Countries [Member] | Infrastructure Solutions [Member]
Revenues		8,161	10,516
Other Foreign Countries [Member] | Corrosion Protection [Member]
Revenues		13,468	17,542
Other Foreign Countries [Member] | Energy Services [Member]
Revenues		$ 0	$ 0

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