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ACCOUNTS RECEIVABLE (Details) - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Receivables [Abstract]        
Accounts receivable $ 229,677 $ 182,728    
Allowance for doubtful accounts (2,974) (3,344) $ (4,527) $ (5,706)
Accounts receivable, net $ 226,703 $ 179,384