Fair Value of Financial Instruments (Details) (Recurring [Member], USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Financial assets measured at fair value on a recurring basis
Assets fair value	$ 81,824	$ 80,329
Liabilities fair value	28,839	26,323
Money Market Funds [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	54,085	54,006
Accrued Liabilities [Member]
Financial assets measured at fair value on a recurring basis
Liabilities fair value	1,100	0
Rabbi Trust [Member] | Mutual funds [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	22,041	25,626
Rabbi Trust [Member] | Money Market Funds [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	5,698	697
Level 1 [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	81,824	80,329
Liabilities fair value	27,739	26,323
Level 1 [Member] | Money Market Funds [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	54,085	54,006
Level 1 [Member] | Payables To Plan Participant [Member]
Financial assets measured at fair value on a recurring basis
Liabilities fair value	27,739	26,323
Level 1 [Member] | Accrued Liabilities [Member]
Financial assets measured at fair value on a recurring basis
Liabilities fair value	0	0
Level 1 [Member] | Rabbi Trust [Member] | Mutual funds [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	22,041	25,626
Level 1 [Member] | Rabbi Trust [Member] | Money Market Funds [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	5,698	697
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] | Money Market Funds [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 2 [Member] | Rabbi Trust [Member] | Mutual funds [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	0	0
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
Level 3 [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	0	0
Liabilities fair value	1,100	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] | 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	1,100	0
Level 3 [Member] | Rabbi Trust [Member] | Mutual funds [Member]
Financial assets measured at fair value on a recurring basis
Assets fair value	0	0
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