Senior Notes (Schedule Of Outstanding Senior Notes) (Details) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Assets Sold under Agreements to Repurchase [Line Items]
Consolidated Balance Sheet Amount	$ 397,134,000	$ 397,074,000
Senior Notes 4.868% [Member] | Senior Notes [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Date Issued	Jun. 05, 2014
Date Due	Jun. 01, 2044	Jun. 01, 2044
Principal Amounts	$ 400,000,000
Consolidated Balance Sheet Amount	397,134,000	$ 397,074,000
Market value	$ 469,804,000	$ 452,848,000