Fair Value Measurements and Financial Instruments Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Jul. 22, 2010
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined benefit pension plan assets	$ 25,754	$ 22,957	$ 22,078
Senior unsecured notes	30,000	30,000		30,000
Long-term debt	50,034	54,787
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined benefit pension plan assets	24,028	20,463
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined benefit pension plan assets	1,726	2,494
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	12,716	10,758
Fuel derivatives, classified as other current assets		0
Defined benefit pension plan assets	24,028	20,463
Fuel derivatives, classified as accrued expenses		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	1,726	2,494
Fuel derivatives, classified as accrued expenses		24
Deferred compensation	1,144	873
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
Fuel derivatives, classified as accrued expenses		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	12,716	10,758
Fuel derivatives, classified as other current assets		38
Defined benefit pension plan assets	25,754	22,957
Fuel derivatives, classified as accrued expenses		24
Deferred compensation	1,144	873
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	0
Fuel derivatives, classified as accrued expenses	0
Revolving credit facility, noncurrent	20,000	24,200
Senior unsecured notes	30,000	30,000
Term loans, noncurrent	34	587
Long-term debt	50,034	54,787
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	20,000	24,200
Senior unsecured notes	28,219	29,762
Term loans, noncurrent	34	587
Long-term debt	$ 48,253	$ 54,549