Annual report pursuant to Section 13 and 15(d)

Receivables and Allowance for Doubtful Receivables (Allowance for Doubtful Receivables Rollforward) (Details)

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Receivables and Allowance for Doubtful Receivables (Allowance for Doubtful Receivables Rollforward) (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Allowance for Doubtful Accounts Receivable [Roll Forward]      
Balance at beginning of year $ 3,630 $ 4,542 $ 2,346
Charged to costs and expenses 8,516 6,359 3,994
Charged to other accounts 0 0 0
Write-offs net of recoveries 7,739 7,271 1,798
Balance at end of year $ 4,407 $ 3,630 $ 4,542