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