Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Financial assets measured at fair value on a recurring basis
Assets held in rabbi trust	$ 34,682	$ 27,739
Level 3 [Member] | Accrued Liabilities [Member]
Financial assets measured at fair value on a recurring basis
Liabilities fair value	8,110	1,100	0
Recurring [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	58,377	81,824
Liabilities fair value	42,792	28,839
Recurring [Member] | Money Market Funds [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	23,695	54,085
Recurring [Member] | Accrued Liabilities [Member]
Financial assets measured at fair value on a recurring basis
Liabilities fair value	8,110	1,100
Recurring [Member] | Rabbi Trust [Member] | Money Market Funds [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	5,737	5,698
Recurring [Member] | Rabbi Trust [Member] | Mutual funds [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	28,945	22,041
Recurring [Member] | Level 1 [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	58,377	81,824
Liabilities fair value	34,682	27,739
Recurring [Member] | Level 1 [Member] | Money Market Funds [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	23,695	54,085
Recurring [Member] | Level 1 [Member] | Payables To Plan Participant [Member]
Financial assets measured at fair value on a recurring basis
Liabilities fair value	34,682	27,739
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	5,737	5,698
Recurring [Member] | Level 1 [Member] | Rabbi Trust [Member] | Mutual funds [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	28,945	22,041
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	8,110	1,100
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	8,110	1,100
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