Investments (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Short-term investments:
Investments, Cost Basis	$ 268,463	$ 285,515
Available-for-sale Securities, Gross Unrealized Gain (Loss)	1,151	1,338
Short-term investments, Fair Value	269,614	286,853
Certificates Of Deposit [Member]
Short-term investments:
Investments, Cost Basis	252,124	269,033
Available-for-sale Securities, Gross Unrealized Gain (Loss)	0	0
Short-term investments, Fair Value	252,124	269,033
U.S. dollar indexed bond funds [Member]
Short-term investments:
Investments, Cost Basis	16,339	16,482
Available-for-sale Securities, Gross Unrealized Gain (Loss)	1,151	1,338
Short-term investments, Fair Value	17,490	17,820
Assets held in rabbi trust [Member]
Long-term investments:
Long-term investments, Cost Basis	6,572	7,428
Long-term investments, Unrealized Gain (Loss)	479	(258)
Fair Value Of Assets Held Under Trust	$ 7,051	$ 7,170