Operating Property Activities (Details Textual) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) properties Landparcels	Jun. 30, 2014 USD ($)
Operating Property Activities (Textual)
Aggregate purchase price			$ 30,000
Decrease of paid in capital			$ 5,400
Number of land parcels | Landparcels			3
Mortgage debt related to property			$ 16,300
Proceeds used to purchase property			$ 31,700
Number of operating properties disposed			54
Disposal or sale of properties	$ 191,100		$ 191,100
Gain on disposition of assets			58,600
Disposed asset impairment charges			$ 1,300
Number of properties held-for-sale | properties			15
Real estate held-for-sale	34,600		$ 34,600
Net of accumulated depreciation	$ 1,000		1,000
Impairment charge on sale of properties			1,300
Impairment charge on adjustment to carrying value of one property			15,800
Remaining interest in Joint Ventures			30,500
Decrease in noncontroling interest			25,000
Impairment charges of real estate investments			21,900	$ 100,000
Impairment of marketable debt securities			800
Gains on change in control of interests		$ 65,598	139,801	$ 69,343
Real Estate Investment [Member]
Operating Property Activities (Textual)
Impairment charges of real estate investments			$ 4,000
Elmont Plaza [Member]
Operating Property Activities (Textual)
Noncontrolling interest by company	50.00%		50.00%
Loss on change in control of interest			$ 200
Kimstone Portfolio [Member]
Operating Property Activities (Textual)
Number of properties acquired | properties			39
Noncontrolling interest by company	33.30%		33.30%
Gains on change in control of interests			$ 140,000