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

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The number of units (items of property) under operating lease arrangements.

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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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Accounting Policies and Basis of Presentation - Narrative (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($) rail_car office_space	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) rail_car office_space	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Accounting Policies [Abstract]
Shipping and handling revenue	$ 3,463	$ 3,939	$ 7,078	$ 8,076
Debt instrument, fair value disclosure	44,372		44,372		$ 37,412
Long-term debt	43,732		43,732		36,001
Unamortized loan fees	$ 485		$ 485		$ 576
Property under operating lease \| Rail cars
Property Subject to or Available for Operating Lease [Line Items]
Property subject to operating leases, number of units \| rail_car	224		224
Property under operating lease \| Office space
Property Subject to or Available for Operating Lease [Line Items]
Property subject to operating leases, number of units \| office_space	1		1