Cash, Cash Equivalents, Short-Term Investments And Fair Value Measurment (Available-For-Sale Securities Reported At Fair Value) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 800,229		$ 801,218
Gross Unrealized Gains	3,039		1,359
Gross Unrealized Losses	(43)		(270)
Estimated Fair Value	803,225		802,307
Less: Restricted cash	(4,870)	[1]	(4,496)	[2]
Total cash, cash equivalents and short-term investments	798,355		797,811
Cash [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	331,902		388,941
Gross Unrealized Gains	0		0
Gross Unrealized Losses	0		0
Estimated Fair Value	331,902		388,941
Level 1 Securities [Member] | Money Market Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	7,618	[1]	123,608	[2]
Gross Unrealized Gains	0	[1]	0	[2]
Gross Unrealized Losses	0	[1]	0	[2]
Estimated Fair Value	7,618	[1]	123,608	[2]
Level 2 Securities [Member] | Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	139,064	[3]	112,264	[4]
Gross Unrealized Gains	1,709	[3]	603	[4]
Gross Unrealized Losses	(3)	[3]	(214)	[4]
Estimated Fair Value	140,770	[3]	112,653	[4]
Level 2 Securities [Member] | US Treasury and Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	202,466	[3]	175,464	[4]
Gross Unrealized Gains	339	[3]	694	[4]
Gross Unrealized Losses	0	[3]	(56)	[4]
Estimated Fair Value	202,805	[3]	176,102	[4]
Level 2 Securities [Member] | Asset And Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	119,179	[3]	941	[4]
Gross Unrealized Gains	991	[3]	62	[4]
Gross Unrealized Losses	(40)	[3]	0	[4]
Estimated Fair Value	120,130	[3]	1,003	[4]
Restricted Cash [Member]
Schedule of Available-for-sale Securities [Line Items]
Less: Restricted cash	(4,900)
Restricted Cash [Member] | Workers Compensation Deposits [Member]
Schedule of Available-for-sale Securities [Line Items]
Less: Restricted cash			(4,500)
Short-term Investments [Member] | Securities Investment [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	428,100
Cash and Cash Equivalents [Member] | Cash And Cash Equivalent [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	2,700		119,100
Cash and Cash Equivalents [Member] | Securities Investment [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	$ 35,600

[1] Includes $2.7 million classified in cash and cash equivalents and $4.9 million of restricted cash classified in other non-current assets.

[2] Includes $119.1 million classified in cash and cash equivalents and $4.5 million of restricted cash classified in other current assets and non-current assets.

[3] Includes $35.6 million classified in cash and cash equivalents and $428.1 million included in short-term investments in the Company’s consolidated balance sheets.

[4] Included in short-term investments.