Shareholders Equity (Details) (USD $) In Thousands, except Share data, unless otherwise specified	6 Months Ended			0 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Jan. 25, 2013 Series L Preferred Stock [Member] Public Offering [Member] Redeemable Preferred Stock [Member]	Feb. 19, 2013 Series H Preferred Stock [Member]	Feb. 19, 2013 Series F And Series H Preferred Stock [Member]
Details Of Preferred Shares Of Beneficial Interest [Abstract]
Preferred shares of beneficial interest: issued shares	52,682,807		51,184,609	12,000,000
Preferred Stock Dividend Rate Percentage				5.40%	6.75%
Preferred Stock, Par or Stated Value Per Share (in Dollars Per Share)				$ 25.00
Aggregate net proceeds after underwriters discounts and issuance costs				$ 290,536
Preferred Stock Issued Additional Disclosure				We retained aggregate net proceeds of $290,536,000, after underwriters’ discounts and issuance costs, and contributed the net proceeds to the Operating Partnership in exchange for 12,000,000 Series L Preferred Units (with economic terms that mirror those of the Series L Preferred Shares).
Purchase Of Outstanding Preferred Units	$ 299,400	$ 0				$ 262,500