Equity And Accumulated Other Comprehensive Loss, Net (Narrative) (Details) (USD $)	0 Months Ended	9 Months Ended			9 Months Ended	12 Months Ended		9 Months Ended			18 Months Ended		9 Months Ended		9 Months Ended
	Jul. 02, 2012	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Sep. 30, 2012 Series F Cumulative Convertible Preferred Units [Member]	Dec. 31, 2012 Series F Cumulative Convertible Preferred Units [Member]	Dec. 31, 2011 Series F Cumulative Convertible Preferred Units [Member]	Sep. 30, 2012 April 5, 2012 [Member] Series F Cumulative Convertible Preferred Units [Member]	Sep. 30, 2012 April 18, 2012 [Member] Series F Cumulative Convertible Preferred Units [Member]	Sep. 30, 2011 2009 Equity Distribution Agreements [Member]	Jun. 30, 2011 2009 Equity Distribution Agreements [Member]	Dec. 31, 2009 2009 Equity Distribution Agreements [Member]	Sep. 30, 2012 2011 Equity Distribution Agreements [Member]	Jun. 29, 2011 2011 Equity Distribution Agreements [Member]	Sep. 30, 2012 Noncontrolling Interests In Consolidated Joint Ventures [Member]
Equity and Accumulated Other Comprehensive Income (Loss) [Line Items]
Net proceeds from issuance of common stock (shares)	11,500,000										6,800,000
Net proceeds from sale of common stock	$ 797,200,000									$ 176,900,000	$ 394,000,000		$ 62,700,000
Conversion of limited partner common units to general partner common units (units)	11,500,000
Aggregate offering price of the distribution agreement maximum												400,000,000		400,000,000
Aggregate shares issued from the distribution agreement										3,000,000
Equity distribution agreements at an average price										$ 60.51			$ 66.19
Payment of commissions to sales agents										2,700,000			600,000
Gross proceeds from the sale of common stock		894,221,000	419,619,000								400,000,000
Issuance of common shares													1,000,000
Issuance date								Apr. 05, 2012	Apr. 18, 2012
Preferred stock, issued					7,300,000		0	7,300,000	7,300,000
Preferred stock, dividend rate					6.625%		6.625%	6.625%	6.625%
Gross proceeds from issuance of redeemable preferred stock								176,200,000	176,200,000
Preferred stock dividend per share amount					$ 1.656	$ 1.65625		$ 1.65625	$ 1.656250
Preferred stock, liquidation preference per share/unit					$ 25.00		$ 25.00	$ 25.00	$ 25.00
Preferred stock, distribution payable date								Jun. 29, 2012	Jun. 29, 2012
Preferred stock, dividends in arrears								$ 0.395660	$ 0.395660
Preferred stock, redemption date								Apr. 05, 2017	Apr. 05, 2017
Preferred stock, redemption price per share								$ 25.00	$ 25.00
Shares issued upon conversion								0.6843	0.684300
Redemption value of OP units		290,100,000		291,500,000
Percentage of operating partnership common units issued		25.00%
Available indebtedness		17,800,000
Date of acquisition															May 04, 2012
Acquisition amount		$ 1,462,200,000													$ 12,400,000