v3.8.0.1
Summary of Significant Accounting Policies - Summary of Changes in the Allowance for Doubtful Accounts (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Accounts Notes Loans And Financing Receivable Gross Allowance And Net [Abstract]      
Beginning balance $ 323 $ 262 $ 631
Provision for doubtful accounts 419 67 647
Write-offs   (6) (1,016)
Ending balance $ 742 $ 323 $ 262