Short-term Investments (Available-For-Sale Securities In A Continuous Unrealized Loss Position) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Fair Value available-for-sale securities Less than 12 Months	$ 659,965	$ 422,786
Unrealized losses, available-for-sale securities, Less than 12 Months	(1,409)	(963)
Fair value available-for-sale securities 12 Months or More	31,927	26,250
Unrealized losses, available-for-sale securities, 12 Months or More	(2,278)	(1,913)
Total Fair Value available-for-sale securities	691,892	449,036
Unrealized losses, available-for-sale securities, Total	(3,687)	(2,876)
U.S. Treasury And Agency Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value available-for-sale securities Less than 12 Months	267,403	221,548
Unrealized losses, available-for-sale securities, Less than 12 Months	(487)	(353)
Fair value available-for-sale securities 12 Months or More	0	0
Unrealized losses, available-for-sale securities, 12 Months or More	0	0
Total Fair Value available-for-sale securities	267,403	221,548
Unrealized losses, available-for-sale securities, Total	(487)	(353)
Corporate And Other Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value available-for-sale securities Less than 12 Months	237,753	106,485
Unrealized losses, available-for-sale securities, Less than 12 Months	(654)	(243)
Fair value available-for-sale securities 12 Months or More	0	0
Unrealized losses, available-for-sale securities, 12 Months or More	0	0
Total Fair Value available-for-sale securities	237,753	106,485
Unrealized losses, available-for-sale securities, Total	(654)	(243)
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value available-for-sale securities Less than 12 Months	140,490	84,051
Unrealized losses, available-for-sale securities, Less than 12 Months	(256)	(333)
Fair value available-for-sale securities 12 Months or More	11,320	5,048
Unrealized losses, available-for-sale securities, 12 Months or More	(132)	(58)
Total Fair Value available-for-sale securities	151,810	89,099
Unrealized losses, available-for-sale securities, Total	(388)	(391)
Municipal Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value available-for-sale securities Less than 12 Months	14,319	10,702
Unrealized losses, available-for-sale securities, Less than 12 Months	(12)	(34)
Fair value available-for-sale securities 12 Months or More	0	1,019
Unrealized losses, available-for-sale securities, 12 Months or More	0	(6)
Total Fair Value available-for-sale securities	14,319	11,721
Unrealized losses, available-for-sale securities, Total	(12)	(40)
Mutual Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value available-for-sale securities Less than 12 Months	0	0
Unrealized losses, available-for-sale securities, Less than 12 Months	0	0
Fair value available-for-sale securities 12 Months or More	20,607	20,183
Unrealized losses, available-for-sale securities, 12 Months or More	(2,146)	(1,849)
Total Fair Value available-for-sale securities	20,607	20,183
Unrealized losses, available-for-sale securities, Total	$ (2,146)	$ (1,849)