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Summary of Significant Accounting Policies - Additional Information (Detail)
 3 Months Ended 6 Months Ended
Jun. 30, 2017
USD ($)
Jun. 30, 2016
USD ($)
Jun. 30, 2017
USD ($)
Customer
Segment
Jun. 30, 2016
USD ($)
Dec. 31, 2016
USD ($)
Significant Accounting Policies [Line Items]          
Number of customers with supply agreement | Customer     5    
Agreements expiring period     2019    
Agreements expiring period     2020    
Rail car revenue recognized $ 1,900,000 $ 1,389,000 $ 3,583,000 $ 2,942,000  
Reservation revenue recognized 7,500,000 2,772,000 15,000,000 5,541,000  
Revenue generated from transportation 11,018,000 121,000 17,622,000 121,000  
Amount related to minimum commitments under customer contracts due or payable 0   $ 0   $ 0
Accounts receivables due period     30 days    
Accounts receivables, allowance for doubtful accounts 0   $ 0   0
Deferred revenue balance 5,000   5,000   1,615,000
Cost of goods sold generated from shipping 10,852,000 157,000 18,154,000 157,000  
Inventory write-down 0 0 0 0  
Amortization of deferred financing cost 117,000 43,000 222,000 80,000  
Accretion of debt discount costs 0 85,000 0 159,000  
Recognized income tax interest and penalties     0    
Probable environmental matters 0   $ 0   0
Number of operating segment | Segment     1    
Revolving Credit Facility          
Significant Accounting Policies [Line Items]          
Long-term Line of Credit 0   $ 0   $ 0
Take-or-pay Contracts          
Significant Accounting Policies [Line Items]          
Revenue recognized for shortfall payments relating to minimum commitments $ 74,000 $ 0 $ 74,000 $ 2,997,000