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Fixed Assets - Textual (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Property, Plant and Equipment [Line Items]      
Depreciation $ 23,873 $ 22,293 $ 18,871
Capital Lease Obligations      
Property, Plant and Equipment [Line Items]      
Capital leased assets, gross 1,903 1,967  
Capital leases, lessee balance sheet, assets by major class, accumulated depreciation $ 1,176 $ 1,316