Accounting Policies (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Revenue Recognition
External freight billed to customers included in revenue	$ 5,200,000	$ 6,500,000
Recurring | Fair value | Cash flows approach
Fair Values of Financial Instruments
Interest rate swap liabilities	(483,000)		(661,000)
Recurring | Significant Other Observable Inputs (Level 2) | Cash flows approach
Fair Values of Financial Instruments
Interest rate swap liabilities	$ (483,000)		$ (661,000)