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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)
 12 Months Ended
Dec. 31, 2018
Accounting Policies [Abstract]  
Schedule of activity in the allowance for doubtful accounts
The following table presents activity in the allowance for doubtful accounts at the dates indicated (in thousands):
 
December 31,
 
2018
 
2017
 
2016
Balance at beginning of period
$
4,893

 
$
7,960

 
$
8,380

Charged to expense
2,083

 
305

 
2,143

Write-offs, net of recoveries
(76
)
 
(3,372
)
 
(2,563
)
Balance at end of period
$
6,900

 
$
4,893

 
$
7,960