Short-Term Investments (Available-For-Sale Securities Reported At Fair Value) (Details) (USD $)	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009	Dec. 31, 2008
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 801,218,000		$ 353,748,000
Gross Unrealized Gains	1,359,000		1,542,000
Gross Unrealized Losses	(270,000)		(342,000)
Estimated Fair Value	802,307,000		354,948,000
Less: Restricted cash	4,496,000	[1]	4,561,000	[2]
Total cash, cash equivalents and short-term investments	797,811,000		350,387,000
Cash and cash equivalents	508,053,000		194,499,000		134,224,000	139,881,000
Cash [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	388,941,000		194,146,000
Estimated Fair Value	388,941,000		194,146,000
Cash And Cash Equivalent [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash and cash equivalents	119,100,000		400,000
Level 1 Securities [Member] | Money Market Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	123,608,000	[1]	4,914,000	[2]
Estimated Fair Value	123,608,000	[1]	4,914,000	[2]
Level 2 Securities [Member] | Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	112,264,000	[3]	109,745,000	[3]
Gross Unrealized Gains	603,000	[3]	1,043,000	[3]
Gross Unrealized Losses	(214,000)	[3]	(101,000)	[3]
Estimated Fair Value	112,653,000	[3]	110,687,000	[3]
Level 2 Securities [Member] | Government And Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	175,464,000	[3]	42,062,000	[3]
Gross Unrealized Gains	694,000	[3]	331,000	[3]
Gross Unrealized Losses	(56,000)	[3]	(101,000)	[3]
Estimated Fair Value	176,102,000	[3]	42,292,000	[3]
Level 2 Securities [Member] | Asset And Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	941,000	[3]	2,881,000	[3]
Gross Unrealized Gains	62,000	[3]	168,000	[3]
Gross Unrealized Losses			(140,000)	[3]
Estimated Fair Value	1,003,000	[3]	2,909,000	[3]
Workers Compensation Deposits [Member]
Schedule of Available-for-sale Securities [Line Items]
Restricted cash other current assets	1,000,000
Long-term restricted cash	$ 3,500,000		$ 4,600,000

[1] Includes $119.1 million that is included in cash and cash equivalents and $3.5 million and $1.0 million of restricted cash that is included in other non-current assets and other current assets, respectively, related to workers compensation deposits.

[2] 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.

[3] Included in short-term investments.