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RECEIVABLES
3 Months Ended
Mar. 31, 2018
Receivables [Abstract]  
RECEIVABLES
RECEIVABLES
A summary of accounts receivable as of March 31, 2018 and December 31, 2017 is as follows (in thousands):
 
 
March 31, 2018
 
December 31, 2017
 
(unaudited)
 
 
Trade accounts receivable
$
209,766

 
$
244,133

Unbilled receivables
92,371

 
69,138

Allowance for doubtful accounts
(13,157
)
 
(11,308
)
Total
$
288,980

 
$
301,963