Short-term Investments (Schedule Of Summary Of Short-Term Investments) (Details) (USD $)	6 Months Ended		12 Months Ended
	Jun. 30, 2012		Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	$ 232,090,000		$ 103,380,000
Available-for-sale Securities, Gross Unrealized Gains	1,102,000	[1]	893,000	[1]
Available-for-Sale Securities, Gross Unrealized Losses	(69,000)	[1]	(67,000)	[1]
Available-for-Sale Securities, Estimated Fair Value	233,123,000		104,206,000
Other Comprehensive Income Unrealized Holding Gain On Securities Arising During Period Net Of Tax	600,000		500,000
Other Comprehensive Income Unrealized Holding Loss On Securities Held In the NQ Deferred Compensation Plan Net Of Tax	600,000		1,800,000
Certificates of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	3,000,000
Available-for-sale Securities, Gross Unrealized Gains	0	[1]
Available-for-Sale Securities, Gross Unrealized Losses	0	[1]
Available-for-Sale Securities, Estimated Fair Value	3,000,000
Obligations Of US Government-Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	38,614,000		40,914,000
Available-for-sale Securities, Gross Unrealized Gains	10,000	[1]	3,000	[1]
Available-for-Sale Securities, Gross Unrealized Losses	(16,000)	[1]	(45,000)	[1]
Available-for-Sale Securities, Estimated Fair Value	38,608,000		40,872,000
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	77,195,000		62,466,000
Available-for-sale Securities, Gross Unrealized Gains	1,086,000	[1]	890,000	[1]
Available-for-Sale Securities, Gross Unrealized Losses	(53,000)	[1]	(22,000)	[1]
Available-for-Sale Securities, Estimated Fair Value	78,228,000		63,334,000
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale Securities, Amortized Cost	113,281,000
Available-for-sale Securities, Gross Unrealized Gains	6,000
Available-for-Sale Securities, Gross Unrealized Losses	0
Available-for-Sale Securities, Estimated Fair Value	$ 113,287,000

[1] he unrealized gains on investments in available-for-sale securities, net of tax effects were $0.6 million and $0.5 million at June 30, 2012 and December 31, 2011, respectively. Additionally, other comprehensive loss included unrealized losses, net of tax effects of $0.6 million and $1.8 million, on investments underlying our 2001 Non-Qualified Deferred Compensation Plan at June 30, 2012 and December 31, 2011, respectively.