INVESTMENTS IN JOINT VENTURES (Narrative) (Details) (USD $)	12 Months Ended								3 Months Ended	12 Months Ended
	Dec. 31, 2013 JointVenture Investment sqft	Dec. 31, 2012 Investment	Dec. 31, 2011	Dec. 31, 2013 Variable Interest Entity, Not Primary Beneficiary [Member] VariableInterestEntity	Dec. 31, 2013 Western United States [Member]	Dec. 31, 2012 Western United States [Member]	Dec. 31, 2013 Minimum [Member]	Dec. 31, 2013 Maximum [Member]	Sep. 30, 2013 European Joint Venture Investments [Member]	Dec. 31, 2013 Joint Venture Properties in UK, Ireland and Spain [Member]	Dec. 31, 2013 KW Residential, LLC [Member] Unit ApartmentBuildling	Dec. 31, 2012 KW Residential, LLC [Member]	Dec. 31, 2011 KW Residential, LLC [Member]	Dec. 31, 2012 Bay Area Smart Growth Fund II, LLC [Member]	Dec. 31, 2013 Bay Area Smart Growth Fund II, LLC [Member]	Dec. 31, 2013 Joint Ventures, Own Retail Properties [Member] Investment	Dec. 31, 2013 Loans Payable [Member] Performance Guarantee [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage							5.00%	50.00%			41.00%			5.00%
Partnership Agreement, Majority Shareholder Requirement, Percentage of Aggregate Commitments														50.00%
Recognized gain in excess of purchase price									$ 36,200,000
Investments in joint ventures	751,400,000	543,200,000			388,900,000	362,500,000					68,800,000	102,700,000
Equity in joint venture income	29,800,000	21,500,000	12,500,000
Acquisition-related expenses	(1,600,000)	(700,000)								(13,500,000)
Equity Method Investments	724,200,000	518,900,000												12,900,000	13,300,000
Number of real estate properties											50
Number of units in portfolio											2,400
Foreign currency exchange gain (loss)	(2,200,000)	3,000,000	(2,600,000)								(6,900,000)	1,200,000	2,500,000
Area of real estate property	68,000,000
Acquisition related gains	56,600,000	25,500,000	6,300,000
Contributions to joint ventures	322,700,000	178,600,000	105,400,000
Proceeds from equity method investments, operating and investing	137,600,000										26,000,000	11,400,000	11,200,000
Payments to Acquire Interest in Joint Venture	57,200,000	29,100,000	41,800,000
Payments to acquired equity method investments, new investments	265,500,000	149,500,000	63,600,000
Number of investments greater than 50% owned without significant influence																3
Cost method investment, number of investments	3	4
Operating distributions from joint ventures	56,100,000	40,400,000	13,000,000		26,700,000						9,400,000	9,600,000	3,300,000
Refinancing of property level debt											5,800,000	1,800,000	5,800,000
Equity method investments, non-managing member ownership percentage														49.50%
Variable Interest Entity, Not Primary Beneficiary, Disclosures [Abstract]
Variable interest entity, number of investments				5
Variable interest entities assets				189,600,000
Variable interest entities maximum loss exponsure				72,600,000
Cost method investments	7,600,000	5,700,000
Unfulfilled capital commitments	8,000,000	8,300,000
Number with unfulfilled capital commitments	4
Guarantees, maximum exposure	$ 51,100,000	$ 55,500,000															$ 51,100,000
Guarantor obligations, maximum exposure, percentage of property level debt																	2.00%