Fair Value Measurements and Financial Instruments Fair Value of Derivatives (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended							3 Months Ended	12 Months Ended						12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Change During Period, Fair Value Disclosure [Member]	Dec. 31, 2012 Change During Period, Fair Value Disclosure [Member]	Dec. 31, 2013 Carrying (Reported) Amount, Fair Value Disclosure [Member]	Dec. 31, 2012 Carrying (Reported) Amount, Fair Value Disclosure [Member]	Dec. 31, 2012 Longest remaining term, in months [Member]	Dec. 31, 2013 Longest remaining term, in months [Member]	Dec. 31, 2013 Notional hedged volume, in thousands of gallons [Member] gal	Dec. 31, 2012 Notional hedged volume, in thousands of gallons [Member] gal	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 1 [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 2 [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2013 Interest Rate Cash Flow Hedges	Dec. 31, 2012 Interest Rate Cash Flow Hedges	Dec. 31, 2011 Interest Rate Cash Flow Hedges
Derivatives, Fair Value [Line Items]
Asset fair value of fuel derivatives, classified as other current assets						$ 0						$ 0	$ 38	$ 0
Liability fair value of fuel derivatives, classified as accrued expenses						0						0	24	0
Liability fair value of fuel derivatives, classified as other noncurrent liabilities						0	0
Longest remaining term, in months								12 months	0 months
Notional hedged volume, in thousands of gallons										0	1,250,000
Hedge gains, recognized in other comprehensive income	0	123	917	0	123										0	123	917
Change in fair value, recognized in results of operations, as a reduction in costs and expenses, operating				$ 139	$ 650