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Revenues (Details) - USD ($)
$ in Thousands
Mar. 31, 2018
Jan. 01, 2018
Dec. 31, 2017
Revenue from Contract with Customer [Abstract]      
Contract with Customer, Refund Liability   $ 1,500  
Allowance for Doubtful Accounts Receivable, Current $ 4,932   $ 9,909
allowance for fallouts and billing adjustments     $ 3,100