Note 12 - Segment Reporting (Details Textual) $ in Thousands		3 Months Ended				6 Months Ended
		Jun. 30, 2020 USD ($)		Jun. 30, 2019 USD ($)		Jun. 30, 2020 USD ($)		Jun. 30, 2019 USD ($)
Number of Reportable Segments						3
Impairment of Long-Lived Assets to be Disposed of						$ 0		$ 11,946
Goodwill, Impairment Loss		$ 1,258		$ 0		1,258	[1]	0
Impairment of Intangible Assets, Finite-lived		957		0		957		0
Infrastructure Solutions [Member]
Impairment of Long-Lived Assets to be Disposed of						700		9,000
Goodwill, Impairment Loss	[1]					(0)
Corrosion Protection [Member]
Impairment of Long-Lived Assets to be Disposed of								2,900
Goodwill, Impairment Loss	[1]					(0)
Energy Services [Member]
Goodwill, Impairment Loss		1,300				1,258	[1]
Impairment of Intangible Assets, Finite-lived						1,000
Restructuring 2017 [Member]
Restructuring Charges, Total		4,833	[2]	6,516	[3]	8,456	[4]	9,382	[5]
Restructuring 2017 [Member] | Operating Income (Loss) [Member] | Infrastructure Solutions [Member]
Restructuring Charges, Total		100		1,400		500		3,400
Restructuring 2017 [Member] | Operating Income (Loss) [Member] | Infrastructure Solutions [Member] | Divestiture of International Operations [Member]
Restructuring Charges, Total		0		400		200		500
Restructuring 2017 [Member] | Operating Income (Loss) [Member] | Corrosion Protection [Member]
Restructuring Charges, Total		1,300		3,300		3,100		3,500
Restructuring 2017 [Member] | Operating Income (Loss) [Member] | Energy Services [Member]
Restructuring Charges, Total		3,500		100		3,600		100
Restructuring 2017 [Member] | Operating Income (Loss) [Member] | Corporate Segment [Member]
Restructuring Charges, Total		900		900		1,600		1,300
Restructuring 2017 [Member] | Operating Income (Loss) [Member] | Corporate Segment [Member] | Divestiture of International Operations [Member]
Restructuring Charges, Total		700		400		1,300		400
Restructuring 2017 [Member] | Other Nonoperating Income (Expense) [Member]
Restructuring Charges, Total		$ 900		$ 900		300		$ 1,100
Restructuring 2017 [Member] | Other Nonoperating Income (Expense) [Member] | Divestiture of International Operations [Member]
Restructuring Charges, Total						$ 700

[1] During the second quarter of 2020, the Company recorded a $1.3 million goodwill impairment related to restructuring activities in Energy Services (see Note 4).

[2] Total pre-tax restructuring charges for the quarter ended June 30, 2020, include cash charges of $2.6 million and non-cash charges of $2.2 million. Cash charges consist of charges incurred during the quarter that will be settled in cash, either during the current period or future periods.

[3] Total pre-tax restructuring charges for the quarter ended June 30, 2019, include cash charges of $5.4 million and non-cash charges of $1.1 million. Cash charges consist of charges incurred during the quarter that will be settled in cash, either during the current period or future periods.

[4] Total pre-tax restructuring charges for the six months ended June 30, 2020, include cash charges of $5.8 million and non-cash charges of $2.7 million. Cash charges consist of charges incurred during the quarter that will be settled in cash, either during the current period or future periods.

[5] Total pre-tax restructuring charges for the six months ended June 30, 2019, include cash charges of $8.5 million and non-cash charges of $0.9 million. Cash charges consist of charges incurred during the quarter that will be settled in cash, either during the current period or future periods.