Equity, Capital and Other Interests Equity, Capital and Other Interests Text (Details) (USD $)	3 Months Ended	12 Months Ended
	Jun. 30, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Stock Repurchased During Period, Shares		0
Additional Common Shares Authorized		6,000,000
Stock Issued During Period, Shares, New Issues		3,200,000	3,900,000	6,200,000
Average Price Per Common Share Issued		$ 60.59	$ 52.23	$ 47.45
Stock Issued During Period, Value, New Issues		$ 192,300,000	$ 201,900,000	$ 291,900,000
Payments of Stock Issuance Costs		39,359,000	3,596,000	4,657,000
Units Issued During Period New Issues		3,200,000	3,900,000	6,200,000
Common Stock Capital Shares Reserved For Future Issuance Under Share Offering Program		17,000,000
Common Shares Added To Atm Program		5,700,000
Shares not settled			500,000
Consideration From Shares Not Settled			28,500,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized		12,980,741
Stock Repurchase Program, Remaining Authorized Repurchase Amount		464,600,000
Repurchased and retired		0	0	(58,130)
Treasury Stock Acquired, Average Cost Per Share				$ 32.46
Value Of Stock Repurchased And Retired				1,900,000
Issuance Of Units To Noncontrolling Interests		1,081,797		188,571
Price Per Unit Issued		$ 61.57		$ 39.15
Properties acquired	1	9	21	1
Proceeds from Issuance of Common Limited Partners Units		66,600,000		7,400,000
Partially Owned Properties Acquired Properties		1	3	2
Partially Owned Units Acquired Units			1,351	432
Business Acquisition, Cost of Acquired Entity, Purchase Price		1,047,545,000	1,597,111,000
Reduction Of Paid In Capital		1,300,000	4,800,000	16,900,000
Reduction In Partially Owned Properties		1,300,000	8,000,000	200,000
Partially owned development projects acquired from outside partner				1
Land parcels acquired from outside partner				1
Issuance Of Units To Noncontrolling Interests to Buyout Interest				1,129
Issue Price Operating Partnership Unit		66,600,000	0	8,200,000
partially owned properties increase in ownership number of properties				3
Issuance Price OP Units to Increase Ownership				800,000
Cash Consideration Equity Buyout				15,300,000
Reduction In Other Liabilities				200,000
Public Offering [Member]
Stock Issued During Period, Shares, New Issues		21,850,000
Average Price Per Common Share Issued		$ 54.75
Stock Issued During Period, Value, New Issues		1,160,400,000
Payments of Stock Issuance Costs		35,900,000
Units Issued During Period New Issues		21,850,000
General And Limited Partner [Member]
Repurchased and retired		0	0	(58,130)
Partner Buyout [Member]
Business Acquisition, Cost of Acquired Entity, Purchase Price			12,800,000	700,000
Issue Price Operating Partnership Unit				50,000
Joint Venture Partner [Member]
Business Acquisition, Cost of Acquired Entity, Purchase Price			$ 75,700,000
Issuance Of Units To Noncontrolling Interests to Buyout Interest				15,948