Note 8 - Goodwill and Intangible Assets - Reconciliation Goodwill (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Goodwill, gross		$ 318,913	$ 317,106	$ 320,904
Accumulated impairment losses		(108,248)	(108,248)	(108,248)
Goodwill, Ending Balance		210,665	208,858	212,656
Foreign currency translation		1,807	426
Reclassification to assets held for sale (1)	[1]		(4,224)
Infrastructure Solutions [Member]
Goodwill, gross		241,719	240,160	244,521
Accumulated impairment losses		(62,848)	(62,848)	(62,848)
Goodwill, Ending Balance		178,871	177,312	181,673
Foreign currency translation		1,559	(137)
Reclassification to assets held for sale (1)	[1]		(4,224)
Corrosion Protection [Member]
Goodwill, gross		77,194	76,946	76,383
Accumulated impairment losses		(45,400)	(45,400)	(45,400)
Goodwill, Ending Balance		31,794	31,546	$ 30,983
Foreign currency translation		$ 248	563
Reclassification to assets held for sale (1)	[1]		$ 0

[1] During 2019, the Company classified certain assets of its CIPP contracting operation in Europe as held for sale (see Note 6).