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Valuation and Qualifying Accounts (Tables)
 12 Months Ended
Dec. 31, 2017
Valuation and Qualifying Accounts [Abstract]  
Schedule of Valuation and Qualifying Accounts
Balance at
Beginning of
Year		      Charged to
Expense		      Deductions
(1)		     Balance at
End of
Year		  

Allowance for doubtful accounts receivable:

           

Year ended December 31, 2017

    $ 5,918        18,478        (18,489 )    $ 5,907  

Year ended December 31, 2016

    $ 5,137        18,639        (17,858 )    $ 5,918  

Year ended December 31, 2015

    $ 6,472        16,620        (17,955 )    $ 5,137  

 

(1) Deductions represent accounts written off, net of recoveries.