Accounting Policies (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014 Fair Value, Measurements, Recurring [Member] Estimate of Fair Value Measurement [Member] Income Approach Valuation Technique [Member]	Dec. 31, 2013 Fair Value, Measurements, Recurring [Member] Estimate of Fair Value Measurement [Member] Income Approach Valuation Technique [Member]	Jun. 30, 2014 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] Income Approach Valuation Technique [Member]	Dec. 31, 2013 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member] Income Approach Valuation Technique [Member]
Revenue Recognition
External freight billed to customers included in revenue	$ 6,800,000	$ 6,600,000	$ 13,400,000	$ 12,700,000
Fair Values of Financial Instruments
Interest rate swap liabilities					$ (1,087,000)	$ (1,533,000)	$ (1,087,000)	$ (1,533,000)