General - Fair Value of Identified Assets and Liabilities (Details) $ in Thousands, £ in Millions	Mar. 01, 2017 GBP (£)	Mar. 01, 2017 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Business Acquisition [Line Items]
Goodwill			$ 261,018	$ 260,715
Environmental Techniques
Business Acquisition [Line Items]
Receivables and cost and estimated earnings in excess of billings		$ 801
Inventories		1,281
Prepaid expenses and other current assets		93
Property, plant and equipment		2,147
Identified intangible assets		1,869
Deferred income tax assets		124
Accounts payable		(1,025)
Accrued expenses		(186)
Deferred income tax liabilities		(413)
Total identifiable net assets		4,691
Total consideration recorded	£ 6.5	8,000
Less: total identifiable net assets		4,691
Goodwill		$ 3,355