Fair Value Measurements and Financial Instruments Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Jul. 22, 2010
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined benefit pension plan assets	$ 22,957	$ 22,078	$ 23,867
Senior unsecured notes	30,000	30,000		30,000
Long-term debt	54,787	51,136
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined benefit pension plan assets	20,463	19,895
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined benefit pension plan assets	2,494	2,183
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined benefit pension plan assets	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets invested for self-insurance, classified as other assets, noncurrent	10,758	13,064
Fuel derivatives, classified as other current assets	0
Defined benefit pension plan assets	20,463	19,895
Interest rate swaps, classifieds as accrued expenses		0
Fuel derivatives, classified as accrued expenses	0	0
Fuel derivatives, classified as other noncurrent liabilities		0
Deferred compensation	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets invested for self-insurance, classified as other assets, noncurrent	0	0
Fuel derivatives, classified as other current assets	38
Defined benefit pension plan assets	2,494	2,183
Interest rate swaps, classifieds as accrued expenses		123
Fuel derivatives, classified as accrued expenses	24	108
Fuel derivatives, classified as other noncurrent liabilities		317
Deferred compensation	873	684
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets invested for self-insurance, classified as other assets, noncurrent	0	0
Fuel derivatives, classified as other current assets	0
Defined benefit pension plan assets	0	0
Interest rate swaps, classifieds as accrued expenses		0
Fuel derivatives, classified as accrued expenses	0	0
Fuel derivatives, classified as other noncurrent liabilities		0
Deferred compensation	0	0
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets invested for self-insurance, classified as other assets, noncurrent	10,758	13,064
Fuel derivatives, classified as other current assets	38
Defined benefit pension plan assets	22,957	22,078
Interest rate swaps, classifieds as accrued expenses		123
Fuel derivatives, classified as accrued expenses	24	108
Fuel derivatives, classified as other noncurrent liabilities		317
Deferred compensation	873	684
Carrying (Reported) Amount, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fuel derivatives, classified as other current assets	38	0
Interest rate swaps, classifieds as accrued expenses	0	123
Fuel derivatives, classified as accrued expenses	24	108
Fuel derivatives, classified as other noncurrent liabilities	0	317
Revolving credit facility, noncurrent	24,200	20,000
Senior unsecured notes	30,000	30,000
Term loans, noncurrent	588	1,136
Long-term debt	54,788	51,136
Portion at Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Revolving credit facility, noncurrent	24,200	20,000
Senior unsecured notes	29,762	29,925
Term loans, noncurrent	588	1,135
Long-term debt	$ 54,550	$ 51,060