Note 12 - Segment Reporting (Details Textual) $ in Thousands	3 Months Ended					9 Months Ended
	Sep. 30, 2019 USD ($)		Jun. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)		Sep. 30, 2019 USD ($)		Sep. 30, 2018 USD ($)
Number of Reportable Segments						3
Restructuring Charges, Total	$ 1,400			$ 1,200		$ 5,500		$ 4,500
Impairment of Long-Lived Assets to be Disposed of	0		$ 11,900	0		11,946		0
Infrastructure Solutions [Member]
Impairment of Long-Lived Assets to be Disposed of						9,000
Corrosion Protection [Member]
Impairment of Long-Lived Assets to be Disposed of						2,900
Restructuring 2017 [Member]
Restructuring Charges, Total	8,607	[1]		7,423	[2]	17,989	[3]	15,580	[4]
Restructuring 2017 [Member] | Corporate, Non-Segment [Member]
Restructuring Charges, Total	1,646			264		2,906		875
Restructuring 2017 [Member] | Operating Income (Loss) [Member] | Corporate, Non-Segment [Member]
Restructuring Charges, Total	1,100			300		2,400		900
Restructuring 2017 [Member] | Operating Income (Loss) [Member] | Divestiture of International Operations [Member] | Corporate, Non-Segment [Member]
Restructuring Charges, Total	1,300			3,100		1,600		3,900
Restructuring 2017 [Member] | Operating Income (Loss) [Member] | Infrastructure Solutions [Member]
Restructuring Charges, Total	1,200			5,900		4,700		11,700
Restructuring 2017 [Member] | Operating Income (Loss) [Member] | Infrastructure Solutions [Member] | Divestiture of International Operations [Member]
Restructuring Charges, Total	500			100		1,000		400
Restructuring 2017 [Member] | Operating Income (Loss) [Member] | Corrosion Protection [Member]
Restructuring Charges, Total	800			1,000		4,300		2,800
Restructuring 2017 [Member] | Operating Income (Loss) [Member] | Corrosion Protection [Member] | Divestiture of International Operations [Member]
Restructuring Charges, Total	100			1,600		100		1,800
Restructuring 2017 [Member] | Other Nonoperating Income (Expense) [Member]
Restructuring Charges, Total	$ 5,300			200		$ 6,500		200
Restructuring 2017 [Member] | Other Nonoperating Income (Expense) [Member] | Bayou [Member]
Restructuring Charges, Total				$ 8,700				$ 8,700

[1] Total pre-tax restructuring charges for the quarter ended September 30, 2019, include cash charges of $3.1 million and non-cash charges of $5.5 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 September 30, 2018, include cash charges of $2.3 million and non-cash charges of $5.1 million. Cash charges consist of charges incurred during the quarter that will be settled in cash, either during the current period or future periods.

[3] Total pre-tax restructuring charges include cash charges of $11.6 million and non-cash charges of $6.4 million. Cash charges consist of charges incurred during the period that will be settled in cash, either during the current period or future periods.

[4] Total pre-tax restructuring charges include cash charges of $7.4 million and non-cash charges of $8.2 million. Cash charges consist of charges incurred during the period that will be settled in cash, either during the current period or future periods.