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Prepaid Expenses and Other Current Assets - Schedule of Prepaid Expenses and Other Current Assets (Detail) - USD ($)
$ in Thousands
Jun. 30, 2018
Dec. 31, 2017
Prepaid Expense and Other Assets [Abstract]    
Prepaid insurance $ 403 $ 551
Prepaid expenses 1,576 1,112
Prepaid income taxes 1,751 1,382
Rail rebate receivables 502 776
Other receivables 597 28
Total prepaid expenses and other current assets $ 4,829 $ 3,849