Investments (Estimated Fair Value Of Investments With Unrealized Losses) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-sale securities, Period of continuous unrealized loss, 12 Months or less, Fair value	$ 84,805	$ 122,581
Available-for-sale securities, Period of continuous unrealized loss, 12 Months or less, Gross unrealized losses	(4)	(11)
Available-for-sale securities, Period of continuous unrealized loss, Greater than 12 months, Fair value		13,031
Available-for-sale securities, Period of continuous unrealized loss, Greater than 12 months, Gross unrealized losses		(1,419)
U.S. Treasury Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-sale securities, Period of continuous unrealized loss, 12 Months or less, Fair value	80,234	122,581
Available-for-sale securities, Period of continuous unrealized loss, 12 Months or less, Gross unrealized losses	(3)	(11)
Corporate Obligations [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-sale securities, Period of continuous unrealized loss, 12 Months or less, Fair value	4,571
Available-for-sale securities, Period of continuous unrealized loss, 12 Months or less, Gross unrealized losses	(1)
Auction Rate Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Available-for-sale securities, Period of continuous unrealized loss, Greater than 12 months, Fair value		13,031
Available-for-sale securities, Period of continuous unrealized loss, Greater than 12 months, Gross unrealized losses		$ (1,419)