Note 7 - Goodwill and Intangible Assets - Reconciliation Goodwill (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020		Jun. 30, 2019	Dec. 31, 2019
Goodwill, gross		$ 397,787		$ 397,787			$ 398,610
Accumulated impairment losses		(143,033)		(143,033)			(141,775)
Goodwill, net		254,754		254,754			256,835
Impairment (1)		(1,258)	$ 0	(1,258)	[1]	$ 0
Foreign currency translation				(823)
Infrastructure Solutions [Member]
Goodwill, gross		239,724		239,724			240,160
Accumulated impairment losses		(62,848)		(62,848)			(62,848)
Goodwill, net		176,876		176,876			177,312
Impairment (1)	[1]			0
Foreign currency translation				(436)
Corrosion Protection [Member]
Goodwill, gross		76,559		76,559			76,946
Accumulated impairment losses		(45,400)		(45,400)			(45,400)
Goodwill, net		31,159		31,159			31,546
Impairment (1)	[1]			0
Foreign currency translation				(387)
Energy Services [Member]
Goodwill, gross		81,504		81,504			81,504
Accumulated impairment losses		(34,785)		(34,785)			(33,527)
Goodwill, net		46,719		46,719			$ 47,977
Impairment (1)		$ (1,300)		(1,258)	[1]
Foreign currency translation				$ 0

[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).