Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Level 3 [Member] | Accrued Liabilities [Member]
Financial assets measured at fair value on a recurring basis
Liabilities fair value	$ 8,202	$ 8,110
Recurring [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	57,974	58,377
Liabilities fair value	43,093	42,792
Recurring [Member] | Money Market Funds [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	23,083	23,695
Recurring [Member] | Payables To Plan Participant [Member]
Financial assets measured at fair value on a recurring basis
Liabilities fair value	34,891	34,682
Recurring [Member] | Accrued Liabilities [Member]
Financial assets measured at fair value on a recurring basis
Liabilities fair value	8,202	8,110
Recurring [Member] | Rabbi Trust [Member] | Money Market Funds [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	4,965	5,737
Recurring [Member] | Rabbi Trust [Member] | Mutual funds [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	29,926	28,945
Recurring [Member] | Level 1 [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	57,974	58,377
Liabilities fair value	34,891	34,682
Recurring [Member] | Level 1 [Member] | Money Market Funds [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	23,083	23,695
Recurring [Member] | Level 1 [Member] | Payables To Plan Participant [Member]
Financial assets measured at fair value on a recurring basis
Liabilities fair value	34,891	34,682
Recurring [Member] | Level 1 [Member] | Accrued Liabilities [Member]
Financial assets measured at fair value on a recurring basis
Liabilities fair value	0	0
Recurring [Member] | Level 1 [Member] | Rabbi Trust [Member] | Money Market Funds [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	4,965	5,737
Recurring [Member] | Level 1 [Member] | Rabbi Trust [Member] | Mutual funds [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	29,926	28,945
Recurring [Member] | Level 2 [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	0	0
Liabilities fair value	0	0
Recurring [Member] | Level 2 [Member] | Money Market Funds [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	0	0
Recurring [Member] | Level 2 [Member] | Payables To Plan Participant [Member]
Financial assets measured at fair value on a recurring basis
Liabilities fair value	0	0
Recurring [Member] | Level 2 [Member] | Accrued Liabilities [Member]
Financial assets measured at fair value on a recurring basis
Liabilities fair value	0	0
Recurring [Member] | Level 2 [Member] | Rabbi Trust [Member] | Money Market Funds [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	0	0
Recurring [Member] | Level 2 [Member] | Rabbi Trust [Member] | Mutual funds [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	0	0
Recurring [Member] | Level 3 [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	0	0
Liabilities fair value	8,202	8,110
Recurring [Member] | Level 3 [Member] | Money Market Funds [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	0	0
Recurring [Member] | Level 3 [Member] | Payables To Plan Participant [Member]
Financial assets measured at fair value on a recurring basis
Liabilities fair value	0	0
Recurring [Member] | Level 3 [Member] | Accrued Liabilities [Member]
Financial assets measured at fair value on a recurring basis
Liabilities fair value	8,202	8,110
Recurring [Member] | Level 3 [Member] | Rabbi Trust [Member] | Money Market Funds [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	0	0
Recurring [Member] | Level 3 [Member] | Rabbi Trust [Member] | Mutual funds [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	$ 0	$ 0