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
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Change During Period, Fair Value Disclosure [Member]	Dec. 31, 2011 Change During Period, Fair Value Disclosure [Member]	Dec. 31, 2012 Carrying (Reported) Amount, Fair Value Disclosure [Member]	Dec. 31, 2011 Carrying (Reported) Amount, Fair Value Disclosure [Member]	Dec. 31, 2012 Longest remaining term, in months [Member]	Dec. 31, 2011 Longest remaining term, in months [Member]	Dec. 31, 2012 Notional hedged volume, in thousands of gallons [Member] gal	Dec. 31, 2011 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, 2011 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, 2011 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, 2011 Fair Value, Measurements, Recurring [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2012 Interest Rate Cash Flow Hedges	Dec. 31, 2011 Interest Rate Cash Flow Hedges	Dec. 31, 2010 Interest Rate Cash Flow Hedges
Derivatives, Fair Value [Line Items]
Liability fair value of interest rate swaps, classified as accrued expenses						$ 0	$ 123						$ 0		$ 123		$ 0
Notional amount of long-term debt hedged						0	10,000
Asset fair value of fuel derivatives, classified as other current assets						38	0					0		38		0
Liability fair value of fuel derivatives, classified as accrued expenses						24	108					0	0	24	108	0	0
Liability fair value of fuel derivatives, classified as other noncurrent liabilities						0	317						0		317		0
Longest remaining term, in months								12 months	24 months
Notional hedged volume, in thousands of gallons										1,250,000	2,500,000
Hedge gains, recognized in other comprehensive income	123	917	315	123														123	917	315
Change in fair value, recognized in results of operations, as a (reduction)/increase in costs and expenses, operating				$ (650)	$ 425