Goodwill and Identified Intangible Assets - Goodwill (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2017 USD ($)
Goodwill [Roll Forward]
Goodwill, gross	$ 393,615
Accumulated impairment losses	(94,996)
Goodwill, beginning balance	298,619
Additions to goodwill through acquisitions	3,355
Foreign currency translation	2,383
Goodwill, gross	399,353
Accumulated impairment losses	(94,996)
Goodwill, ending balance	304,357
Environmental Techniques
Goodwill [Roll Forward]
Additions to goodwill through acquisitions	3,400
Infrastructure Solutions
Goodwill [Roll Forward]
Goodwill, gross	239,494
Accumulated impairment losses	(16,069)
Goodwill, beginning balance	223,425
Additions to goodwill through acquisitions	3,355
Foreign currency translation	2,147
Goodwill, gross	244,996
Accumulated impairment losses	(16,069)
Goodwill, ending balance	228,927
Corrosion Protection
Goodwill [Roll Forward]
Goodwill, gross	73,875
Accumulated impairment losses	(45,400)
Goodwill, beginning balance	28,475
Additions to goodwill through acquisitions	0
Foreign currency translation	236
Goodwill, gross	74,111
Accumulated impairment losses	(45,400)
Goodwill, ending balance	28,711
Energy Services
Goodwill [Roll Forward]
Goodwill, gross	80,246
Accumulated impairment losses	(33,527)
Goodwill, beginning balance	46,719
Additions to goodwill through acquisitions	0
Foreign currency translation	0
Goodwill, gross	80,246
Accumulated impairment losses	(33,527)
Goodwill, ending balance	$ 46,719