Note 12 - Segment Reporting (Details Textual)	3 Months Ended				6 Months Ended
	Jun. 30, 2019 USD ($)		Jun. 30, 2018 USD ($)		Jun. 30, 2019 USD ($)		Jun. 30, 2018 USD ($)
Number of Reportable Segments					3
Restructuring Charges, Total	$ 3,000,000.0		$ 1,500,000		$ 4,100,000		$ 3,300,000
Impairment of Long-Lived Assets to be Disposed of	11,946,000		0		11,946,000		0
Operating Income (Loss) [Member] | Infrastructure Solutions [Member]
Impairment of Long-Lived Assets to be Disposed of					9,000,000.0
Operating Income (Loss) [Member] | Corrosion Protection [Member]
Impairment of Long-Lived Assets to be Disposed of	2,900,000
Restructuring 2017 [Member]
Restructuring Charges, Total	6,516,000	[1]	2,913,000	[2]	9,382,000	[3]	8,157,000	[4]
Restructuring 2017 [Member] | Corporate, Non-Segment [Member]
Restructuring Charges, Total	906,000		48,000		1,260,000		611,000
Restructuring 2017 [Member] | Operating Income (Loss) [Member] | Corporate, Non-Segment [Member]
Restructuring Charges, Total	900,000		100,000		1,300,000		600,000
Restructuring 2017 [Member] | Operating Income (Loss) [Member] | Divestiture of International Operations [Member] | Corporate, Non-Segment [Member]
Restructuring Charges, Total	400,000		500,000		400,000		800,000
Restructuring 2017 [Member] | Operating Income (Loss) [Member] | Infrastructure Solutions [Member]
Restructuring Charges, Total	1,400,000		2,500,000		3,400,000		5,700,000
Restructuring 2017 [Member] | Operating Income (Loss) [Member] | Infrastructure Solutions [Member] | Divestiture of International Operations [Member]
Restructuring Charges, Total	400,000		200,000		0.5		0.2
Restructuring 2017 [Member] | Operating Income (Loss) [Member] | Corrosion Protection [Member]
Restructuring Charges, Total	3,300,000		300,000		3,500,000		1,800,000
Restructuring 2017 [Member] | Operating Income (Loss) [Member] | Corrosion Protection [Member] | Divestiture of International Operations [Member]
Restructuring Charges, Total	100,000		$ 100,000		100,000		$ 200,000
Restructuring 2017 [Member] | Other Nonoperating Income (Expense) [Member]
Restructuring Charges, Total	$ 900,000				$ 1,100,000

[1] 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.

[2] Total pre-tax restructuring charges for the quarter ended June 30, 2018, include cash charges of $2.3 million and non-cash charges of $0.6 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 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.

[4] Total pre-tax restructuring charges include cash charges of $5.2 million and non-cash charges of $3.0 million. Cash charges consist of charges incurred during the quarter that will be settled in cash, either during the current period or future periods.