Short-Term Investments And Fair Value Measurement (Available-For-Sale Securities Reported At Fair Value) (Details) (USD $) In Thousands	Sep. 30, 2011		Jun. 30, 2011	Dec. 31, 2010		Sep. 30, 2010	Jun. 30, 2010	Dec. 31, 2009
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	$ 368,963	[1]		$ 353,748	[1]
Gross Unrealized Gains	1,542	[1]		1,542	[1]
Gross Unrealized Losses	(171)	[1]		(342)	[1]
Total Estimated Fair Value	370,334	[1]		354,948	[1]
Less: Long-term restricted cash	(4,562)	[2]		(4,561)	[3]
Total cash, cash equivalents and short-term investments	365,772			350,387
Cash and cash equivalents	159,199		175,207	194,499		113,108	107,327	134,224
Level 1 Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash and cash equivalents	2,000
Level 1 Securities [Member] | Money Market Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,532	[2]		4,914	[3]
Gross Unrealized Gains		[2]			[3]
Gross Unrealized Losses		[2]			[3]
Estimated Fair Value, Money market funds	6,532	[2]		4,914	[3]
Level 2 Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash and cash equivalents				400
Level 2 Securities [Member] | Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	116,569	[1]		109,745	[1]
Gross Unrealized Gains	743	[1]		1,043	[1]
Gross Unrealized Losses	(171)	[1]		(101)	[1]
Estimated Fair Value	117,141	[1]		110,687	[1]
Level 2 Securities [Member] | Government And Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	87,663	[1]		42,062	[1]
Gross Unrealized Gains	740	[1]		331	[1]
Gross Unrealized Losses		[1]		(101)	[1]
Estimated Fair Value	88,403	[1]		42,292	[1]
Level 2 Securities [Member] | Asset And Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	970	[1]		2,881	[1]
Gross Unrealized Gains	59	[1]		168	[1]
Gross Unrealized Losses		[1]		(140)	[1]
Estimated Fair Value	1,029	[1]		2,909	[1]
Cash [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	157,229			194,146
Gross Unrealized Gains
Gross Unrealized Losses
Estimated Fair Value, Cash	$ 157,229			$ 194,146

[1] Included in short-term investments.

[2] Includes $2.0 million that is included in cash and cash equivalents and $4.6 million of long-term restricted cash that is included in other non-current assets related to workers compensation deposits.

[3] Includes $0.4 million that is included in cash and cash equivalents and $4.6 million of long-term restricted cash that is included in other non-current assets related to workers compensation deposits.