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ALLOWANCE FOR DOUBTFUL ACCOUNTS
 12 Months Ended
Dec. 31, 2016
ALLOWANCE FOR DOUBTFUL ACCOUNTS [Abstract]  
ALLOWANCE FOR DOUBTFUL ACCOUNTS
ALLOWANCE FOR DOUBTFUL ACCOUNTS

The following table shows the activity in the allowance for doubtful accounts (in thousands of dollars):
 
For the Years Ended December 31,
 
2016
 
2015
Balance at beginning of period
$
22,288

 
$
22,121

Provision for uncollectible accounts
16,216

 
10,181

Write-off of uncollectible accounts, net of recoveries
(11,248
)
 
(10,495
)
Business acquisitions, foreign currency and other
(566
)
 
481

Balance at end of period
$
26,690

 
$
22,288