Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Roll Forward of Receivable Allowance (Details)

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Summary of Significant Accounting Policies - Roll Forward of Receivable Allowance (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Allowance for Doubtful Accounts Receivable [Roll Forward]      
Balance Beginning of Year $ 3,043 $ 2,762 $ 2,120
Charged to Expense 11,014 10,785 9,735
Write-Offs and Other (9,895) (10,504) (9,093)
Balance End of Year $ 4,162 $ 3,043 $ 2,762