Goodwill and Intangible Assets - Reconciliation Goodwill (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Roll Forward]
Goodwill, gross - beginning balance		$ 401,101	$ 393,615
Goodwill, accumulated impairment loss - beginning balance		(140,386)	(94,996)
Goodwill, net - beginning balance		260,715	298,619
Additions to goodwill through acquisitions		3,973	3,355
Goodwill impairment		(1,389)	(45,390)	$ 0
Foreign currency translation		(2,666)	4,131
Goodwill, gross - ending balance		402,408	401,101	393,615
Goodwill, accumulated impairment loss - ending balance		(141,775)	(140,386)	(94,996)
Goodwill, net - ending balance		260,633	260,715	298,619
Environmental Techniques
Goodwill [Roll Forward]
Additions to goodwill through acquisitions			3,400
Hebna
Goodwill [Roll Forward]
Additions to goodwill through acquisitions		2,700
P2S
Goodwill [Roll Forward]
Additions to goodwill through acquisitions		1,300
Infrastructure Solutions
Goodwill [Roll Forward]
Goodwill, gross - beginning balance		246,486	239,494
Goodwill, accumulated impairment loss - beginning balance		(61,459)	(16,069)
Goodwill, net - beginning balance		185,027	223,425
Additions to goodwill through acquisitions		0	3,355
Goodwill impairment	$ (45,400)	(1,389)	(45,390)
Foreign currency translation		(1,965)	3,637
Goodwill, gross - ending balance		244,521	246,486	239,494
Goodwill, accumulated impairment loss - ending balance		(62,848)	(61,459)	(16,069)
Goodwill, net - ending balance		181,673	185,027	223,425
Corrosion Protection
Goodwill [Roll Forward]
Goodwill, gross - beginning balance		74,369	73,875
Goodwill, accumulated impairment loss - beginning balance		(45,400)	(45,400)
Goodwill, net - beginning balance		28,969	28,475
Additions to goodwill through acquisitions		2,715	0
Goodwill impairment		0	0
Foreign currency translation		(701)	494
Goodwill, gross - ending balance		76,383	74,369	73,875
Goodwill, accumulated impairment loss - ending balance		(45,400)	(45,400)	(45,400)
Goodwill, net - ending balance		30,983	28,969	28,475
Energy Services
Goodwill [Roll Forward]
Goodwill, gross - beginning balance		80,246	80,246
Goodwill, accumulated impairment loss - beginning balance		(33,527)	(33,527)
Goodwill, net - beginning balance		46,719	46,719
Additions to goodwill through acquisitions		1,258	0
Goodwill impairment		0	0
Foreign currency translation		0	0
Goodwill, gross - ending balance		81,504	80,246	80,246
Goodwill, accumulated impairment loss - ending balance		(33,527)	(33,527)	(33,527)
Goodwill, net - ending balance		47,977	46,719	$ 46,719
Fyfe
Goodwill [Roll Forward]
Goodwill, net - beginning balance		9,600
Goodwill, net - ending balance			$ 9,600
Denmark | Infrastructure Solutions
Goodwill [Roll Forward]
Goodwill impairment		$ (1,400)