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Basis of Presentation and Summary of Significant Accounting Policies - Allowance for Doubtful Accounts (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Allowance for Doubtful Accounts Receivable [Roll Forward]      
Allowance for doubtful accounts, beginning balance $ 1,577 $ 2,473 $ 2,057
Provision for doubtful accounts 4,940 2,646 3,693
Amounts written off (3,685) (3,542) (3,277)
Allowance for doubtful accounts, ending balance $ 2,832 $ 1,577 $ 2,473