Investments (Details) (USD $) In Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2011	Dec. 31, 2010
Short-term investments:
Investments, Cost Basis	$ 263,062	$ 274,420
Investments, Unrealized Gain (Loss)	(1,833)	(1,297)
Short-term investments	261,229	273,123
Certificates Of Deposit [Member]
Short-term investments:
Investments, Cost Basis	229,532	221,706
Short-term investments	229,532	221,706
U.S. dollar indexed bond funds [Member]
Short-term investments:
Investments, Cost Basis	33,530	52,714
Investments, Unrealized Gain (Loss)	(1,833)	(1,297)
Short-term investments	31,697	51,417
Assets held in rabbi trust [Member]
Long-term investments:
Long-term investments, Cost Basis	7,920	8,068
Long-term investments, Unrealized (Gain) Loss	480	95
Long-term investments, Fair Value	$ 8,400	$ 8,163