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Allowance for Doubtful Accounts
 12 Months Ended
Dec. 31, 2015
Allowance for Doubtful Accounts [Abstract]  
Allowance for Doubtful Accounts
14. Allowance for Doubtful Accounts

Activity in the allowance for doubtful accounts is summarized as follows for the years presented (in thousands):

  
Year Ended December 31,
 
  
2015
  
2014
  
2013
 
Balance, beginning of year
 
$
911
  
$
763
  
$
724
 
Charges to expense
  
455
   
934
   
280
 
Uncollected balances written off, net of recoveries
  
(617
)
  
(786
)
  
(241
)
Balance, end of year
 
$
749
  
$
911
  
$
763