Business Segments (Details Textual) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011 Investment	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011 Segments	Dec. 31, 2010	Dec. 31, 2009
Segment Reporting Information [Line Items]
Total revenues	$ 484,132,000	$ 488,641,000	$ 327,235,000	$ 233,283,000	$ 236,223,000	$ 222,944,000	$ 213,606,000	$ 211,814,000	$ 1,533,291,000	$ 884,587,000	$ 1,027,171,000
Number of investments in property funds			2
Impairment Charges			97,000,000						21,237,000	736,612,000	331,592,000
Impairment of goodwill										368,451,000
Business Segments (Textual) [Abstract]
Number of reportable segments									2
Private capital [Member]
Segment Reporting Information [Line Items]
Total revenues									137,619,000	122,526,000	144,963,000
Direct owned [Member]
Segment Reporting Information [Line Items]
Total revenues									1,395,672,000	762,061,000	701,971,000
Real estate operations segment [Member]
Segment Reporting Information [Line Items]
Assets held for sale	444,900,000				554,200,000				444,900,000	554,200,000
Americas [Member]
Segment Reporting Information [Line Items]
Assets held for sale					20,600,000					20,600,000
Americas [Member] | Private capital [Member]
Segment Reporting Information [Line Items]
Total revenues									76,872,000	66,653,000	67,964,000
Americas [Member] | Direct owned [Member]
Segment Reporting Information [Line Items]
Total revenues									890,135,000	587,911,000	594,365,000
Americas [Member] | Real estate operations segment [Member]
Segment Reporting Information [Line Items]
Assets held for sale	79,100,000				470,500,000				79,100,000	470,500,000
Europe [Member] | Private capital [Member]
Segment Reporting Information [Line Items]
Total revenues									46,087,000	54,835,000	50,814,000
Europe [Member] | Direct owned [Member]
Segment Reporting Information [Line Items]
Total revenues									344,249,000	91,458,000	62,477,000
Europe [Member] | Real estate operations segment [Member]
Segment Reporting Information [Line Items]
Assets held for sale	332,500,000				18,200,000				332,500,000	18,200,000
Asia [Member] | Private capital [Member]
Segment Reporting Information [Line Items]
Total revenues									14,660,000	1,038,000	26,185,000
Asia [Member] | Direct owned [Member]
Segment Reporting Information [Line Items]
Total revenues									161,288,000	82,692,000	45,129,000
Asia [Member] | Real estate operations segment [Member]
Segment Reporting Information [Line Items]
Assets held for sale	33,300,000				65,500,000				33,300,000	65,500,000
North America [Member]
Segment Reporting Information [Line Items]
Impairment of goodwill										235,500,000
U.S. [Member]
Segment Reporting Information [Line Items]
Total revenues									891,100,000	611,400,000	588,300,000
Long-lived assets attributable to the United States	$ 11,800,000,000				$ 8,600,000,000				$ 11,800,000,000	$ 8,600,000,000