Quarterly report pursuant to Section 13 or 15(d)

Shareholders' Equity (Schedule Of Preferred Stock Outstanding) (Details)

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Shareholders' Equity (Schedule Of Preferred Stock Outstanding) (Details) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Mar. 31, 2021
Dec. 31, 2020
Class of Stock [Line Items]    
Shares Outstanding 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% 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% 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% 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% 4.875%
Shares Outstanding 13,000 13,000
Shares Amount $ 325,000 $ 325,000