Accounting Policies (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 Recurring Fair value Cash flows approach	Dec. 31, 2012 Recurring Fair value Cash flows approach	Sep. 30, 2013 Recurring Significant Other Observable Inputs (Level 2) Cash flows approach	Dec. 31, 2012 Recurring Significant Other Observable Inputs (Level 2) Cash flows approach
Revenue Recognition
External freight billed to customers included in revenue	$ 7,100,000	$ 6,700,000	$ 19,800,000	$ 20,500,000
Fair Values of Financial Instruments
Interest rate swap liabilities					$ (1,777,000)	$ (2,629,000)	$ (1,777,000)	$ (2,629,000)