Annual report pursuant to Section 13 and 15(d)

Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Summary of Changes in Allowance for Doubtful Accounts (Detail)

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Summary of Significant Accounting Policies - Summary of Changes in Allowance for Doubtful Accounts (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Receivables [Abstract]      
Beginning balance – allowance for doubtful accounts $ 13,699 $ 4,759 $ 4,180
Provision for doubtful accounts 18,649 11,856 2,318
Write-offs (18,648) (2,916) (1,739)
Ending balance – allowance for doubtful accounts $ 13,700 $ 13,699 $ 4,759