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Trade Accounts Receivable - Summary of Trade Accounts Receivable (Detail) - USD ($)
$ in Thousands
Jun. 30, 2017
Dec. 31, 2016
Accounts Receivable Net Current [Abstract]    
Trade accounts receivable $ 3,912 $ 5,093
Allowance for doubtful accounts (15) (15)
Trade accounts receivable, net 3,897 5,078
Unpaid deferred revenue included in trade accounts receivable $ 747 $ 2,245