Fair Value Measurements (Fair Values Of Held-To-Maturity Marketable Securities) (Details) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
Maturity Less Than 1 Year [Member] | Amortized Cost [Member]
Debt securities	$ 67,755	$ 469,318
Maturity Less Than 1 Year [Member] | Estimated Fair Value [Member]
Debt securities	68,303	469,956
Maturity Between 1 to 5 Years [Member] | Amortized Cost [Member]
Debt securities	120,164	120,078
Maturity Between 1 to 5 Years [Member] | Estimated Fair Value [Member]
Debt securities	121,556	121,406
Amortized Cost [Member]
Debt securities	187,919	589,396
Estimated Fair Value [Member]
Debt securities	$ 189,859	$ 591,362