Goodwill and Intangible Assets - Goodwill (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Goodwill [Roll Forward]
Goodwill, gross	$ 403,532			$ 403,532		$ 401,101
Accumulated impairment losses	(141,775)			(141,775)		(140,386)
Goodwill, beginning balance				260,715
Acquisitions				3,973
Goodwill impairment	1,389		$ 45,390	1,389	$ 45,390
Foreign currency translation				(1,542)
Goodwill, ending balance	261,757			261,757
Infrastructure Solutions
Goodwill [Roll Forward]
Goodwill, gross	245,123			245,123		246,486
Accumulated impairment losses	(62,848)			(62,848)		(61,459)
Goodwill, beginning balance				185,027
Acquisitions				0
Goodwill impairment			$ 45,400	1,389	$ 45,400
Foreign currency translation				(1,363)
Goodwill, ending balance	182,275			182,275
Corrosion Protection
Goodwill [Roll Forward]
Goodwill, gross	76,905			76,905		74,369
Accumulated impairment losses	(45,400)			(45,400)		(45,400)
Goodwill, beginning balance				28,969
Acquisitions				2,715
Goodwill impairment				0
Foreign currency translation				(179)
Goodwill, ending balance	31,505			31,505
Energy Services
Goodwill [Roll Forward]
Goodwill, gross	81,504			81,504		80,246
Accumulated impairment losses	(33,527)			(33,527)		$ (33,527)
Goodwill, beginning balance				46,719
Goodwill impairment				0
Foreign currency translation				0
Goodwill, ending balance	47,977			$ 47,977
Hebna | Corrosion Protection
Goodwill [Roll Forward]
Acquisitions		$ 2,700
Energy Services
Goodwill [Roll Forward]
Acquisitions	1,258
Denmark | Infrastructure Solutions
Goodwill [Roll Forward]
Goodwill impairment	$ 1,400