Short-Term Investments (Schedule Of Gross Unrealized Losses And Fair Value Of Investments) (Details) (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	$ 141,376
Unrealized Losses, Less than 12 Months	(257)
Fair Value, 12 Months or Greater	5,223
Unrealized Losses, 12 Months or Greater	(37)
Fair Value, Total	146,599
Unrealized Losses, Total	(294)	(73)
U.S. Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	23,341
Unrealized Losses, Less than 12 Months	(5)
Fair Value, Total	23,341
Unrealized Losses, Total	(5)
Obligations Of U.S. Government-Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	46,142
Unrealized Losses, Less than 12 Months	(62)
Fair Value, 12 Months or Greater	5,223
Unrealized Losses, 12 Months or Greater	(37)
Fair Value, Total	51,365
Unrealized Losses, Total	(99)	(50)
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	71,324
Unrealized Losses, Less than 12 Months	(189)
Fair Value, Total	71,324
Unrealized Losses, Total	(189)	(23)
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	569
Unrealized Losses, Less than 12 Months	(1)
Fair Value, Total	569
Unrealized Losses, Total	$ (1)