Short-term Investments (Available-For-Sale Securities Reported At Fair Value) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Total, Amortized Cost	$ 1,672,517	[1]	$ 1,204,938	[2]
Total, Unrealized Gains	1,656	[1]	1,761	[2]
Total, Unrealized Losses	(227)	[1]	(1,092)	[2]
Total, Estimated Fair Value	1,673,946	[1]	1,205,607	[2]
Cash and Cash Equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Estimated Fair Value	1,157,500		605,000
Short-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Estimated Fair Value	510,800		595,400
Non-current Assets [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Estimated Fair Value	5,700		5,200
Level 1 Securities [Member] | Money market funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash, Money market and Government and agency securities classified as cash equivalents, Amortized Cost	94,103		126,208
Cash, Money market and Government and agency securities classified as cash equivalents, Gross Unrealized Gains	0		0
Cash, Money market and Government and agency securities classified as cash equivalents, Gross Unrealized Losses	0		0
Cash, Money market and Government and agency securities classified as cash equivalents, Estimated Fair Value	94,103		126,208
Level 2 Securities [Member] | Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost	328,233		316,465
Available-for-sale Securities, Gross Unrealized Gains	1,333		1,245
Available-for-sale Securities, Gross Unrealized Losses	(218)		(654)
Available-for-sale Securities, Estimated Fair Value	329,348		317,056
Level 2 Securities [Member] | Government securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost	136,374		143,812
Available-for-sale Securities, Gross Unrealized Gains	319		287
Available-for-sale Securities, Gross Unrealized Losses	(9)		(18)
Available-for-sale Securities, Estimated Fair Value	136,684		144,081
Level 2 Securities [Member] | Asset and mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost	3,382		93,118
Available-for-sale Securities, Gross Unrealized Gains	4		229
Available-for-sale Securities, Gross Unrealized Losses	0		(418)
Available-for-sale Securities, Estimated Fair Value	3,386		92,929
Level 2 Securities [Member] | Certificates of deposits [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost	23,425		23,425
Available-for-sale Securities, Gross Unrealized Gains	0		0
Available-for-sale Securities, Gross Unrealized Losses	0		0
Available-for-sale Securities, Estimated Fair Value	23,425		23,425
Level 2 Securities [Member] | Agency securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost	17,950		17,951
Available-for-sale Securities, Gross Unrealized Gains	0		0
Available-for-sale Securities, Gross Unrealized Losses	0		(2)
Available-for-sale Securities, Estimated Fair Value	17,950		17,949
Cash [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash, Money market and Government and agency securities classified as cash equivalents, Amortized Cost	1,069,050		483,959
Cash, Money market and Government and agency securities classified as cash equivalents, Gross Unrealized Gains	0		0
Cash, Money market and Government and agency securities classified as cash equivalents, Gross Unrealized Losses	0		0
Cash, Money market and Government and agency securities classified as cash equivalents, Estimated Fair Value	$ 1,069,050		$ 483,959

[1] Includes $1,157.5 million that is included in cash and cash equivalents, $510.8 million included in short-term investments and $5.7 million of restricted cash that is included in other non-current assets related to workers compensation deposits.

[2] Includes $605.0 million that is included in cash and cash equivalents, $595.4 million included in short-term investments and $5.2 million of restricted cash that is included in other non-current assets related to workers compensation deposits.