Senior Notes (Schedule Of Outstanding Senior Notes) (Details) - Senior Notes [Member] - USD ($)	6 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
4.868% Senior notes due 6/1/2044 [Member]
Debt Instrument [Line Items]
Debt instrument, stated interest rate	4.868%	4.868%
Date issued	Jun. 05, 2014
Date due	Jun. 01, 2044
Principal amounts	$ 400,000,000
Consolidated balance sheet amount	400,000,000	$ 400,000,000
Market value	$ 388,680,000	$ 404,892,000
5.4% Senior notes due 10/15/2014 [Member]
Debt Instrument [Line Items]
Debt instrument, stated interest rate	5.40%
Date issued	Oct. 12, 2004
Date due	Oct. 15, 2014
Principal amounts	$ 250,000,000