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Trade Accounts Receivable - Summary of Trade Accounts Receivable (Detail) - USD ($)
$ in Thousands
Mar. 31, 2018
Dec. 31, 2017
Accounts Receivable Net Current [Abstract]    
Trade accounts receivable $ 3,805 $ 6,419
Allowance for doubtful accounts (15) (15)
Trade accounts receivable, net 3,790 6,404
Unpaid deferred revenue included in trade accounts receivable $ 909 $ 2,217