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Description of Business and Summary of Significant Accounting Policies - Allowance for Doubtful Accounts (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 period $ 12 $ 15 $ 65
Add: bad debt expense 95 75 171
Less: write-offs, net of recoveries (74) (78) (221)
Balance, end of period $ 33 $ 12 $ 15