Unconsolidated Entities (Details 2) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Schedule of Equity Method Investments [Line Items]
Investments in and advances to unconsolidated entities	$ 2,220,172	$ 2,857,755
Co-investment ventures [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage in co-investment ventures	25.70%	27.90%
Investments in and advances to unconsolidated entities	1,943,843	2,471,179
Co-investment ventures [Member] | Americas [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage in co-investment ventures	24.30%	28.20%
Investments in and advances to unconsolidated entities	1,119,279	1,596,295
Co-investment ventures [Member] | Europe [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage in co-investment ventures	30.40%	29.90%
Investments in and advances to unconsolidated entities	633,674	662,010
Co-investment ventures [Member] | Asia [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage in co-investment ventures	19.30%	19.40%
Investments in and advances to unconsolidated entities	$ 190,890	$ 212,874