Investments (Available-For-Sale Securities In A Continuous Unrealized Loss Position) (Details) (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Schedule of Available-for-sale Securities [Line Items]
Fair value available-for-sale securities less than twelve months	$ 275,112	$ 261,882
Unrealized losses available-for-sale securities less than twelve months	(1,086)	(942)
Fair value available-for-sale securities twelve months or longer	2,866
Unrealized losses available-for-sale securities twelve months or longer	(103)
Total fair value available-for-sale securities	277,978
Total unrealized losses of available-for-sale securities	(1,189)
U.S. Treasury And Agency Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value available-for-sale securities less than twelve months	126,897	200,772
Unrealized losses available-for-sale securities less than twelve months	(330)	(592)
Total fair value available-for-sale securities	126,897
Total unrealized losses of available-for-sale securities	(330)
Corporate And Other Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value available-for-sale securities less than twelve months	87,974	16,518
Unrealized losses available-for-sale securities less than twelve months	(585)	(63)
Total fair value available-for-sale securities	87,974
Total unrealized losses of available-for-sale securities	(585)
Asset-Backed Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value available-for-sale securities less than twelve months	50,255	17,791
Unrealized losses available-for-sale securities less than twelve months	(141)	(137)
Fair value available-for-sale securities twelve months or longer	827
Unrealized losses available-for-sale securities twelve months or longer	(10)
Total fair value available-for-sale securities	51,082
Total unrealized losses of available-for-sale securities	(151)
Municipal Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value available-for-sale securities less than twelve months	8,472	25,598
Unrealized losses available-for-sale securities less than twelve months	(28)	(149)
Fair value available-for-sale securities twelve months or longer	2,039
Unrealized losses available-for-sale securities twelve months or longer	(93)
Total fair value available-for-sale securities	10,511
Total unrealized losses of available-for-sale securities	(121)
Foreign Government Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair value available-for-sale securities less than twelve months	1,514	1,203
Unrealized losses available-for-sale securities less than twelve months	(2)	(1)
Total fair value available-for-sale securities	1,514
Total unrealized losses of available-for-sale securities	$ (2)