Quarterly report pursuant to Section 13 or 15(d)

Revenue - Accounts Receivable, Net (Details)

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Revenue - Accounts Receivable, Net (Details) - USD ($)
$ in Thousands
Sep. 30, 2018
Dec. 31, 2017
Sep. 30, 2017
Dec. 31, 2016
Revenue from Contract with Customer [Abstract]        
Accounts receivable, gross $ 104,471 $ 122,225    
Less: Allowance for doubtful accounts (4,793) (8,680) $ (12,195) $ (10,091)
Accounts receivable, net $ 99,678 $ 113,545