Shareholders' Equity (Schedule Of Preferred Stock Outstanding) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Class of Stock [Line Items]
Shares Outstanding	37,790	37,790	37,790	37,790
Shares Amount	$ 944,750	$ 944,750
Series W Preferred Stock [Member]
Class of Stock [Line Items]
Issuance Date	Oct. 01, 2016
Earliest Potential Redemption Date	Oct. 01, 2021
Dividend Rate	5.20%
Shares Outstanding	7,590	7,590
Shares Amount	$ 189,750	$ 189,750
Series X Preferred Stock [Member]
Class of Stock [Line Items]
Issuance Date	Sep. 01, 2017
Earliest Potential Redemption Date	Sep. 01, 2022
Dividend Rate	5.25%
Shares Outstanding	9,200	9,200
Shares Amount	$ 230,000	$ 230,000
Series Y Preferred Stock [Member]
Class of Stock [Line Items]
Issuance Date	Dec. 01, 2017
Earliest Potential Redemption Date	Dec. 01, 2022
Dividend Rate	5.20%
Shares Outstanding	8,000	8,000
Shares Amount	$ 200,000	$ 200,000
Series Z Preferred Stock [Member]
Class of Stock [Line Items]
Issuance Date	Nov. 01, 2019
Earliest Potential Redemption Date	Nov. 01, 2024
Dividend Rate	4.875%
Shares Outstanding	13,000	13,000
Shares Amount	$ 325,000	$ 325,000