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ALLOWANCE FOR DOUBTFUL ACCOUNTS (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
ALLOWANCE FOR DOUBTFUL ACCOUNTS [Abstract]      
Balance at beginning of period $ 26,690 $ 22,288  
Provision for uncollectible accounts 16,376 16,216 $ 10,181
Write-off of uncollectible accounts, net of recoveries (16,597) (11,248)  
Business acquisitions, foreign currency and other 2,798 (566)  
Balance at end of period $ 29,267 $ 26,690 $ 22,288