Accounting Policies and Basis of Presentation - Narrative (Detail) $ in Thousands	3 Months Ended
Mar. 31, 2017 USD ($) rail_car office_space	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)
Accounting Policies [Abstract]
Shipping and handling revenue	$ 3,614	$ 4,137
Debt instrument, fair value disclosure	44,887		$ 37,412
Long-term debt	43,693		36,001
Unamortized loan fees	$ 530		$ 576
Rail Cars [Member] \| Property Subject to Operating Lease [Member]
Property Subject to or Available for Operating Lease [Line Items]
Property subject to operating leases, number of units \| rail_car	218
Office Space [Member] \| Property Subject to Operating Lease [Member]
Property Subject to or Available for Operating Lease [Line Items]
Property subject to operating leases, number of units \| office_space	1

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Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

+ References

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Fees charged to customers for the delivery, generally by postal or freight service providers, of product or goods purchased.

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