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Summary of Significant Accounting Policies - Schedule of Roll Forward of Company's Allowance for Doubtful Accounts (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Receivables [Abstract]      
Allowance for doubtful accounts, Beginning Balance $ 638 $ 617 $ 371
Allowance for doubtful accounts, Charged to Statement of Operations 5,514 3,353 2,517
Allowance for doubtful accounts, Deductions (4,835) (3,332) (2,271)
Allowance for doubtful accounts, Ending Balance $ 1,317 $ 638 $ 617