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Summary of Significant Accounting Policies - Additional Information (Detail)
 3 Months Ended 9 Months Ended
Sep. 30, 2017
USD ($)
Sep. 30, 2016
USD ($)
Sep. 30, 2017
USD ($)
Customer
Segment
Sep. 30, 2016
USD ($)
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 $ 2,021,000 $ 1,395,000 $ 5,605,000 $ 4,337,000  
Reservation revenue recognized 7,500,000 5,000,000 22,500,000 10,541,000  
Revenue generated from transportation 13,925,000 0 31,547,000 121,000  
Amount related to minimum commitments under customer contracts due or payable 0 0 $ 0 0  
Accounts receivables due period     30 days    
Accounts receivables, allowance for doubtful accounts 0   $ 0   $ 0
Deferred revenue balance 0   0   1,615,000
Cost of goods sold generated from shipping 15,390,000 0 33,544,000 157,000  
Inventory write-down 0 0 0 0  
Amortization of deferred financing cost 116,000 37,000 339,000 117,000  
Accretion of debt discount costs 0 73,000 0 232,000  
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 $ 1,169,000 $ 0 $ 1,244,000 $ 2,997,000