Fair Value Measurements and Financial Instruments Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended										3 Months Ended		6 Months Ended
	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2012 Carrying (reported) amount, fair value disclosure [Member]	Dec. 31, 2011 Carrying (reported) amount, fair value disclosure [Member]	Jun. 30, 2012 Portion at fair value, fair value disclosure [Member]	Dec. 31, 2011 Portion at fair value, fair value disclosure [Member]	Jun. 30, 2012 Longest remaining term, in months [Member]	Dec. 31, 2011 Longest remaining term, in months [Member]	Jun. 30, 2012 Notional hedged volume, in thousands of gallons [Member] gal	Dec. 31, 2011 Notional hedged volume, in thousands of gallons [Member] gal	Jun. 30, 2012 Change during period, fair value disclosure [Member]	Jul. 02, 2011 Change during period, fair value disclosure [Member]	Jun. 30, 2012 Change during period, fair value disclosure [Member]	Jul. 02, 2011 Change during period, fair value disclosure [Member]
Liabilities, Fair Value Disclosure [Abstract]
Revolving credit facility, noncurrent			$ 28,400	$ 20,000	$ 28,400	$ 20,000
Senior unsecured notes	30,000	30,000	30,000	30,000	30,416	29,925
Term loans, noncurrent			715	1,136	715	1,135
Total			59,115	51,136	59,531	51,060
Interest Rate Derivatives, at Fair Value, Net [Abstract]
Liability fair value of interest rate swaps classified as accrued expenses			0	123
Notional amount of long-term debt hedged			0	10,000
Price Risk Derivatives [Abstract]
Liability fair value of fuel derivatives, classified as accrued expenses			306	108
Liability fair value of fuel derivatives, classified as other noncurrent liabilities			237	317
Longest remaining term, in months							18 months	24 months
Notional hedged volume, in thousands of gallons									1,900,000	2,500,000
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net [Abstract]
Hedge gains, recognized in other comprehensive income, Effective Portion, Net	123										0	223	123	441
Gain (Loss) on Fair Value Hedges Recognized in Earnings [Abstract]
Change in fair value, recognized in results of operations, as a decrease in operating costs and expenses											$ (888)	$ 22	$ 34	$ 22