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Valuation and Qualifying Accounts (Note)
 12 Months Ended
Dec. 31, 2018
Valuation and Qualifying Accounts [Abstract]  
Schedule of Valuation and Qualifying Accounts Disclosure [Text Block]
Valuation and Qualifying Accounts

Accounts receivable balances are stated net of allowance for doubtful accounts. Historically, the Company has not experienced significant write-offs. The Company records allowances for doubtful accounts when it is probable that the accounts receivable balance will not be collected. The following table provides a summary of the allowance for doubtful accounts balances and activity for the years ended December 31, 2018, 2017 and 2016:

 
 
Year Ended December 31,
(in thousands)
 
2018
 
2017
 
2016
Beginning balance-allowance for doubtful accounts
 
$
20,958

 
$
18,369

 
$
19,140

Additions-charged to expense
 
8,653

 
6,631

 
6,556

Amounts written off
 
(4,079
)
 
(5,944
)
 
(6,839
)
Other (primarily changes in foreign currency exchange rates)
 
(1,245
)
 
1,902

 
(488
)
Ending balance-allowance for doubtful accounts
 
$
24,287

 
$
20,958

 
$
18,369