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Property, Plant and Equipment - Depreciation and Amortization Expense (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Property, Plant and Equipment [Line Items]    
Depreciation and amortization $ 28,300 $ 31,099
Services    
Property, Plant and Equipment [Line Items]    
Depreciation and amortization 23,579 26,643
Products    
Property, Plant and Equipment [Line Items]    
Depreciation and amortization 1,137 1,309
General and administrative expenses    
Property, Plant and Equipment [Line Items]    
Depreciation and amortization $ 3,584 $ 3,147