Available-For-Sale Securities (Schedule Of Available-For-Sale Securities Portfolio Continuous Unrealized Loss Position) (Details) (USD $) In Thousands	Sep. 30, 2011
Continuous unrealized losses existing for less than 12 months, Fair value	$ 282,747
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(3,703)
Continuous unrealized losses existing for greater than 12 months, Fair value	5,637
Continuous unrealized losses existing for greater than 12 months, Unrealized losses	(1,304)
Total Fair value	288,384
Total Unrealized losses	(5,007)
U.S. Treasury [Member]
Continuous unrealized losses existing for less than 12 months, Fair value
Continuous unrealized losses existing for less than 12 months, Unrealized losses
Continuous unrealized losses existing for greater than 12 months, Fair value
Continuous unrealized losses existing for greater than 12 months, Unrealized losses
Total Fair value
Total Unrealized losses
U.S. Government Agencies [Member]
Continuous unrealized losses existing for less than 12 months, Fair value	175,299
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(224)
Total Fair value	175,299
Total Unrealized losses	(224)
Municipal Securities [Member]
Continuous unrealized losses existing for less than 12 months, Fair value	4,825
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(18)
Total Fair value	4,825
Total Unrealized losses	(18)
Corporate Notes And Other, Financial Issuers [Member]
Continuous unrealized losses existing for less than 12 months, Fair value	87,857
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(3,334)
Continuous unrealized losses existing for greater than 12 months, Fair value	5,637
Continuous unrealized losses existing for greater than 12 months, Unrealized losses	(1,304)
Total Fair value	93,494
Total Unrealized losses	(4,638)
Corporate Notes And Other, Other [Member]
Continuous unrealized losses existing for less than 12 months, Fair value	8,494
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(59)
Total Fair value	8,494
Total Unrealized losses	(59)
Other Equity Securities [Member]
Continuous unrealized losses existing for less than 12 months, Fair value	392
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(60)
Total Fair value	392
Total Unrealized losses	$ (60)