Fair Value of Financial Instruments (Details) (Recurring [Member], USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Financial assets measured at fair value on a recurring basis
Assets fair value	$ 84,595	$ 81,824
Liabilities fair value	33,118	28,839
Mutual funds [Member] | Rabbi Trust [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	27,911	22,041
Money Market Funds [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	51,477	54,085
Money Market Funds [Member] | Rabbi Trust [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	5,207	5,698
Payables To Plan Participant [Member]
Financial assets measured at fair value on a recurring basis
Liabilities fair value	33,118	27,739
Accrued Liabilities [Member]
Financial assets measured at fair value on a recurring basis
Liabilities fair value	0	1,100
Level 1 [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	84,595	81,824
Liabilities fair value	33,118	27,739
Level 1 [Member] | Mutual funds [Member] | Rabbi Trust [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	27,911	22,041
Level 1 [Member] | Money Market Funds [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	51,477	54,085
Level 1 [Member] | Money Market Funds [Member] | Rabbi Trust [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	5,207	5,698
Level 1 [Member] | Payables To Plan Participant [Member]
Financial assets measured at fair value on a recurring basis
Liabilities fair value	33,118	27,739
Level 1 [Member] | Accrued Liabilities [Member]
Financial assets measured at fair value on a recurring basis
Liabilities fair value	0	0
Level 2 [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	0	0
Liabilities fair value	0	0
Level 2 [Member] | Mutual funds [Member] | Rabbi Trust [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	0	0
Level 2 [Member] | Money Market Funds [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	0	0
Level 2 [Member] | Money Market Funds [Member] | Rabbi Trust [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	0	0
Level 2 [Member] | Payables To Plan Participant [Member]
Financial assets measured at fair value on a recurring basis
Liabilities fair value	0	0
Level 2 [Member] | Accrued Liabilities [Member]
Financial assets measured at fair value on a recurring basis
Liabilities fair value	0	0
Level 3 [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	0	0
Liabilities fair value	0	1,100
Level 3 [Member] | Mutual funds [Member] | Rabbi Trust [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	0	0
Level 3 [Member] | Money Market Funds [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	0	0
Level 3 [Member] | Money Market Funds [Member] | Rabbi Trust [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	0	0
Level 3 [Member] | Payables To Plan Participant [Member]
Financial assets measured at fair value on a recurring basis
Liabilities fair value	0	0
Level 3 [Member] | Accrued Liabilities [Member]
Financial assets measured at fair value on a recurring basis
Liabilities fair value	$ 0	$ 1,100