Schedule III Real Estate Rollforward (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Real Estate and Accumulated Depreciation [Line Items]
Real Estate, Gross	$ 6,708,250	$ 6,038,107	$ 7,032,889	$ 6,390,119
Real Estate, Other Acquisitions	658,917	669,631	449,530
Real Estate, Improvements	211,460	184,533	162,301
Real Estate Accumulated Depreciation, Depreciation Expense	262,825	267,222	271,058
Real Estate Accumulated Depreciation	1,296,685	1,127,595	1,406,437	1,311,733
Real Estate, Other Additions	0	5,988	530,573
Real Estate, Period Increase (Decrease)	6,908,484	7,893,041	7,532,523
Real Estate Accumulated Depreciation, Period Increase (Decrease)	1,390,420	1,673,659	1,582,791
Real Estate, Cost of Real Estate Sold	(157,630)	(1,774,576)	(421,325)
Real Estate Accumulated Depreciation, Real Estate Sold	(51,131)	(465,353)	(97,699)
Real Estate Accumulated Depreciation, Other Deductions	$ (42,604)	$ (80,711)	$ (78,655)
Real Estate, Write-down or Reserve, Basis	-42604	-80358	-78309
Leasehold Improvements [Member] | Maximum [Member]
Real Estate and Accumulated Depreciation [Line Items]
Property, Plant and Equipment, Useful Life	10 years
Developed Properties [Member] | Maximum [Member]
Real Estate and Accumulated Depreciation [Line Items]
Property, Plant and Equipment, Useful Life	40 years