Investments in Joint Ventures (Narrative) (Details) (USD $)	3 Months Ended		6 Months Ended				6 Months Ended			3 Months Ended		6 Months Ended			6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 JointVenture	Jun. 30, 2012	Dec. 31, 2012	Jun. 30, 2013 Performance Guarantee [Member] Loans Payable [Member]	Jun. 30, 2013 Variable Interest Entity, Not Primary Beneficiary [Member] VariableInterestEntity	Jun. 30, 2013 Minimum [Member]	Jun. 30, 2013 Maximum [Member]	Jun. 30, 2013 KW Residential, LLC [Member] building Unit	Jun. 30, 2012 KW Residential, LLC [Member]	Jun. 30, 2013 KW Residential, LLC [Member] building Unit	Jun. 30, 2012 KW Residential, LLC [Member]	Dec. 31, 2012 KW Residential, LLC [Member]	Jun. 30, 2013 Class A Office Building and Adjacent 3.5 Acre Site in Dublin Ireland [Member] Irish Commerical Investment Joint Venture [Member]	Apr. 16, 2013 Class A Office Building and Adjacent 3.5 Acre Site in Dublin Ireland [Member] Irish Commerical Investment Joint Venture [Member] acre
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage								5.00%	50.00%	41.00%		41.00%
Investments in joint ventures	$ 694,664,000		$ 694,664,000		$ 543,193,000					$ 76,700,000		$ 76,700,000		$ 102,700,000
Number of properties in portfolio										50		50
Number of units in portfolio										2,400		2,400
Area of real estate property																3.5
Joint venture, acquisition-related gain															30,100,000
Acquisition-related gain	0	0	9,459,000	0											15,000,000
Foreign currency exchange gain (loss)	(1,099,000)	(1,399,000)	(4,978,000)	651,000						(2,500,000)	2,300,000	(6,300,000)	2,100,000
Payments to acquire equity method investment			173,068,000	49,469,000
Proceeds from equity method investments			38,400,000							5,071,000	3,164,000	18,576,000	9,023,000
Payments to joint venture for debt repayment and to fund working capital			43,500,000
Variable Interest Entity, Not Primary Beneficiary, Disclosures [Abstract]
Variable interest entity, number of investments							5
Variable interest entity, carrying amount assets							227,600,000
Variable interest entity, maximum loss exposure							93,000,000
Unfulfilled capital commitments			7,200,000
Unfulfilled capital commitments, number with unfulfilled capital commitments			4
Guarantor obligations, maximum exposure						$ 55,700,000
Guarantor obligations, maximum exposure, percentage of property level debt						2.10%