Short-Term And Long-Term Investments (Schedule Of Unrealized Losses And Related Fair Value, Investments With Unrealized Losses) (Details) (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Short-term Debt [Line Items]
Less Than 12 Months To Maturity, Aggregate Fair Value	$ 54,465	$ 40,375
Less Than 12 Months To Maturity, Unrealized Losses	(117)	(29)
12 Months or More To Maturity, Aggregate Fair Value	71,444	36,578
12 Months or More To Maturity, Unrealized Losses	(197)	(102)
Aggregate Fair Value, Total	125,909	76,953
Unrealized Losses, Total	(314)	(131)
Certificates Of Deposit [Member]
Short-term Debt [Line Items]
Less Than 12 Months To Maturity, Aggregate Fair Value	8,589	13,283
Less Than 12 Months To Maturity, Unrealized Losses	(1)	(21)
12 Months or More To Maturity, Aggregate Fair Value	9,982	1,678
12 Months or More To Maturity, Unrealized Losses	(4)	(1)
Aggregate Fair Value, Total	18,571	14,961
Unrealized Losses, Total	(5)	(22)
Commercial Paper [Member]
Short-term Debt [Line Items]
Less Than 12 Months To Maturity, Aggregate Fair Value	19,196	7,486
Less Than 12 Months To Maturity, Unrealized Losses	(22)	(1)
12 Months or More To Maturity, Aggregate Fair Value	0	0
12 Months or More To Maturity, Unrealized Losses	0	0
Aggregate Fair Value, Total	19,196	7,486
Unrealized Losses, Total	(22)	(1)
Corporate Securities [Member]
Short-term Debt [Line Items]
Less Than 12 Months To Maturity, Aggregate Fair Value	26,680	19,606
Less Than 12 Months To Maturity, Unrealized Losses	(94)	(7)
12 Months or More To Maturity, Aggregate Fair Value	39,142	18,437
12 Months or More To Maturity, Unrealized Losses	(186)	(68)
Aggregate Fair Value, Total	65,822	38,043
Unrealized Losses, Total	(280)	(75)
U.S. Government Agency Securities [Member]
Short-term Debt [Line Items]
Less Than 12 Months To Maturity, Aggregate Fair Value	0	0
Less Than 12 Months To Maturity, Unrealized Losses	0	0
12 Months or More To Maturity, Aggregate Fair Value	22,320	16,463
12 Months or More To Maturity, Unrealized Losses	(7)	(33)
Aggregate Fair Value, Total	22,320	16,463
Unrealized Losses, Total	$ (7)	$ (33)

This item represents the excess of amortized cost basis over fair value of securities that have been in a loss position for twelve months or longer for those securities which are categorized neither as held-to-maturity nor trading securities.

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This item represents the excess of amortized cost basis over fair value of securities in a loss position and which are categorized neither as held-to-maturity nor trading securities.

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This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for less than twelve months.

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