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Prepaid Expenses and Other Current Assets - Schedule of Prepaid Expenses and Other Current Assets (Detail) - USD ($)
$ in Thousands
Mar. 31, 2018
Dec. 31, 2017
Prepaid Expense and Other Assets [Abstract]    
Prepaid insurance $ 589 $ 551
Prepaid expenses 1,342 1,112
Prepaid income taxes 1,458 1,382
Rail rebate receivables 952 776
Other receivables 651 28
Total prepaid expenses and other current assets $ 4,992 $ 3,849