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Schedule II - Valuation and Qualifying Accounts (Tables)
 12 Months Ended
Dec. 31, 2018
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]  
Valuation and qualifying accounts
Description
 
Balance at
Beginning of Period
 
Additions - Charged to
Costs and Expenses
 
Additions - Charged to
Other Accounts - Describe
 
Deductions -
 Describe
 
Balance at
End of Period
Allowance for doubtful accounts:
 
 
 
 
 
 
 
 
 
 
 
For the year ended December 31, 2018
 
$
12,717

 
$
9,475

 
$
—

 
$
8,954

(1) 
 
$
13,238

For the year ended December 31, 2017
 
12,040

 
8,598

 
—

 
7,921

(1) 
 
12,717

For the year ended December 31, 2016
 
$
9,637

 
$
9,587

 
$
—

 
$
7,184

(1) 
 
$
12,040

(1) 
Uncollectable accounts written off.