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Real Estate and Accumulated Depreciation (Details 3) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Real estate assets:      
Balance at beginning of year $ 11,080,161 $ 12,010,668 $ 12,498,513
Acquisitions of operating properties, transfers of development completions from CIP and improvements to operating properties and net affect of changes in foreign exchange rates and other 12,150,482 631,860 1,840,879
Basis of operating properties disposed of (906,602) (1,140,511) (1,145,256)
Change in the development portfolio balance, including the acquisition of properties 0 174,235 (990,217)
Impairment of real estate properties (21,237) (400) (193,251)
Assets transferred to held-for-sale (384,894) (325,691) 0
Balance at end of year 22,413,079 11,080,161 12,010,668
Accumulated Depreciation:      
Depreciation expense 574,524 298,164 275,689
Balances retired upon disposition of operating properties (994) (337,845) (194,128)
Assets transferred to held-for-sale (12,068) (34,301) 0
Balance at beginning of year 1,589,251 1,663,233 1,581,672
Balance at end of year $ 2,150,713 $ 1,589,251 $ 1,663,233