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Allowance for Uncollectible Accounts
 12 Months Ended
Dec. 31, 2017
Valuation and Qualifying Accounts [Abstract]  
Allowance for Uncollectible Accounts
13. Allowance for Uncollectible Accounts
The following table summarizes the activity and ending balances in the allowance for uncollectible accounts for the twelve months ended December 31, 2017, 2016 and 2015 (amounts in thousands):
 
Year
 
Beginning of
Year Balance
 
Additions
 
Deductions
 
End of Year
Balance
2017
 
$
29,036

 
$
9,484

 
$
14,964

 
$
23,556

2016
 
26,712

 
14,790

 
12,466

 
29,036

2015
 
18,582

 
19,243

 
11,113

 
26,712