Net Gain (Loss) on Disposition of Full or Partial Interest in Rental Properties (Details Textual) (USD $)	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Jan. 31, 2012	Jan. 31, 2013	Mar. 31, 2011 properties
Significant Acquisitions and Disposals [Line Items]
Net gain on disposition of partial interest in rental properties	$ (146,000)		$ 386,559,000	$ (613,000)	$ 386,559,000
Acquisitions of noncontrolling interests				83,871,000	101,467,000
QIC Joint Venture [Member]
Significant Acquisitions and Disposals [Line Items]
Percentage of ownership sold			49.00%		49.00%
Number of properties			7		7
Debt assumed by the outside partner			448,900,000		448,900,000
Proceeds received by the Company					412,300,000
Cash proceeds received by the Company					188,200,000
Net gain on disposition of partial interest in rental properties	0		381,627,000	(467,000)	381,627,000
Number of regional retail malls in which Company acquired noncontrolling interests			2
Acquisitions of noncontrolling interests			92,400,000
New York Retail Joint Venture [Member]
Significant Acquisitions and Disposals [Line Items]
Percentage of ownership sold								49.00%
Number of properties								15
Debt assumed by the outside partner								244,952,000
Net gain on disposition of partial interest in rental properties	0	109,533,000	4,932,000	0	4,932,000	9,561,000
Proceeds in the form of loan from the joint venture						178,286,000
Outside partner's minimum initial investment requirement						20.00%
Deferred gain							$ 114,465,000