Fair Value Measurements (Fair Values Of Held-To-Maturity Marketable Securities) (Details) (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Maturity Less Than 1 Year [Member] | Amortized Cost [Member]
Schedule of Held-to-maturity Securities [Line Items]
Debt securities	$ 65,690	$ 469,318
Maturity Less Than 1 Year [Member] | Estimated Fair Value [Member]
Schedule of Held-to-maturity Securities [Line Items]
Debt securities	65,534	469,956
Maturity Between 1 To 5 Years [Member] | Amortized Cost [Member]
Schedule of Held-to-maturity Securities [Line Items]
Debt securities	20,341	120,078
Maturity Between 1 To 5 Years [Member] | Estimated Fair Value [Member]
Schedule of Held-to-maturity Securities [Line Items]
Debt securities	20,284	121,406
Amortized Cost [Member]
Schedule of Held-to-maturity Securities [Line Items]
Debt securities	86,031	589,396
Estimated Fair Value [Member]
Schedule of Held-to-maturity Securities [Line Items]
Debt securities	$ 85,818	$ 591,362