Investments (Schedule Of Available-For-Sale Securities) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Investment [Line Items]
Amortized Cost	$ 1,307,910	$ 876,988
Gross Unrealized Gains	2,401	3,539
Gross Unrealized Losses	(635)	(192)
Fair Value	1,309,676	880,335
Agency securities
Investment [Line Items]
Amortized Cost	453,922	400,365
Gross Unrealized Gains	1,177	2,347
Gross Unrealized Losses	(349)	(5)
Fair Value	454,750	402,707
Corporate securities
Investment [Line Items]
Amortized Cost	643,360	404,546
Gross Unrealized Gains	947	947
Gross Unrealized Losses	(216)	(171)
Fair Value	644,091	405,322
Municipal securities
Investment [Line Items]
Amortized Cost	53,698	32,214
Gross Unrealized Gains	81	114
Gross Unrealized Losses	(23)	(15)
Fair Value	53,756	32,313
Government securities
Investment [Line Items]
Amortized Cost	156,930	39,863
Gross Unrealized Gains	196	131
Gross Unrealized Losses	(47)	(1)
Fair Value	$ 157,079	$ 39,993