Shareholders' Equity/Partners' Capital (Preferred shares of beneficial interest) (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	Nov. 24, 2020	Dec. 31, 2020	Dec. 31, 2019
Details Of Preferred Shares Of Beneficial Interest
Preferred shares/units of beneficial interest: authorized shares		110,000,000	110,000,000
Preferred stock, value		$ 1,182,339	$ 891,214
Preferred shares/units of beneficial interest: outstanding shares		48,793,402	36,795,640
Redeemable Preferred Stock
Details Of Preferred Shares Of Beneficial Interest
Preferred stock, liquidation preference per share		$ 25.00
6.5% Series A | Convertible Preferred Stock
Details Of Preferred Shares Of Beneficial Interest
Preferred stock dividend rate		6.50%
Preferred shares/units of beneficial interest: authorized shares		13,402	15,640
Preferred stock, value		$ 934	$ 991
Preferred shares/units of beneficial interest: outstanding shares		13,402	15,640
Preferred stock, liquidation preference per share		$ 50.00
Preferred stock, dividend rate, per-dollar-amount		$ 3.25
5.70% Series K | Redeemable Preferred Stock
Details Of Preferred Shares Of Beneficial Interest
Preferred stock dividend rate		5.70%
Preferred shares/units of beneficial interest: authorized shares		12,000,000
Preferred stock, value		$ 290,971	$ 290,971
Preferred shares/units of beneficial interest: outstanding shares		12,000,000	12,000,000
Preferred stock, liquidation preference per share		$ 25.00
Preferred stock, dividend rate, per-dollar-amount		$ 1.425
5.40% Series L | Redeemable Preferred Stock
Details Of Preferred Shares Of Beneficial Interest
Preferred stock dividend rate		5.40%
Preferred shares/units of beneficial interest: authorized shares		13,800,000,000
Preferred stock, value		$ 290,306	$ 290,306
Preferred shares/units of beneficial interest: outstanding shares		12,000,000	12,000,000
Preferred stock, liquidation preference per share		$ 25.00
Preferred stock, dividend rate, per-dollar-amount		$ 1.35
5.25% Series M | Redeemable Preferred Stock
Details Of Preferred Shares Of Beneficial Interest
Preferred stock dividend rate		5.25%
Preferred shares/units of beneficial interest: authorized shares		13,800,000
Preferred stock, value		$ 308,946	$ 308,946
Preferred shares/units of beneficial interest: outstanding shares		12,780,000	12,780,000
Preferred stock, liquidation preference per share		$ 25.00
Preferred stock, dividend rate, per-dollar-amount		$ 1.3125
5.25% Series N
Details Of Preferred Shares Of Beneficial Interest
Preferred stock dividend rate	5.25%
5.25% Series N | Redeemable Preferred Stock
Details Of Preferred Shares Of Beneficial Interest
Preferred stock dividend rate	5.25%	5.25%
Preferred shares/units of beneficial interest: authorized shares	12,000,000	12,000,000
Preferred stock, value		$ 291,182	$ 0
Preferred shares/units of beneficial interest: outstanding shares		12,000,000	0
Preferred stock, liquidation preference per share		$ 25.00
Preferred stock, dividend rate, per-dollar-amount		$ 1.3125