Annual report pursuant to Section 13 and 15(d)

Reportable Segments - Capital Expenditures (Details)

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Reportable Segments - Capital Expenditures (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Revenues from External Customers and Long-Lived Assets      
Capital expenditure $ 131,688 $ 140,482 $ 121,421
Operating segments | Performance Materials & Chemicals      
Revenues from External Customers and Long-Lived Assets      
Capital expenditures gross 75,476 84,783 71,293
Operating segments | Environmental Catalysts & Services      
Revenues from External Customers and Long-Lived Assets      
Capital expenditures gross 55,007 53,145 57,803
Eliminations      
Revenues from External Customers and Long-Lived Assets      
Capital expenditures gross $ 1,205 $ 2,554 $ (7,675)