Discontinued Operations and Investment Properties Held for Sale (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended		12 Months Ended	9 Months Ended		0 Months Ended				3 Months Ended	9 Months Ended	0 Months Ended	3 Months Ended	0 Months Ended
	Sep. 30, 2012 property	Sep. 30, 2011 property	Dec. 31, 2011 property	Sep. 30, 2012 Discontinued operations sqft	Sep. 30, 2011 Discontinued operations	Feb. 02, 2012 Jacksonville, FL Discontinued operations sqft	Apr. 10, 2012 Winston-Salem, NC Discontinued operations sqft	Aug. 17, 2012 Stockton, CA Discontinued operations sqft	Sep. 18, 2012 13 former Mervyns properties Discontinued operations property sqft	Sep. 30, 2012 13 former Mervyns properties Discontinued operations	Sep. 30, 2012 13 former Mervyns properties Discontinued operations property	Sep. 25, 2012 Dallas, TX Discontinued operations property sqft	Sep. 30, 2012 Dallas, TX Discontinued operations	Sep. 28, 2012 Ventura, CA Discontinued operations sqft
Discontinued operations
Square footage				2,758,800		13,800	501,000	1,035,800	1,000,400			132,600		75,200
Consideration				$ 219,835		$ 5,800	$ 23,570	$ 63,000	$ 100,400			$ 19,050		$ 8,015
Mortgage debt extinguished				137,123		0	23,570	16,300	97,253			0		0
Net sales proceeds/(outflow)				78,053		5,702	0	46,555	(251)			18,048		7,999
Gain				16,518		915	6,847	8,235	0			0		521
Impairment charges	23,490	31,752		11,507	31,752					1,100			5,528
Mortgage payable	2,396,899		2,926,218						116,400
Number of properties sold	20	6	11						13			3
Number of properties in Mervyns portfolio											23
Proceeds and gains from disposition of real estate properties
Net proceeds from condemnation awards, earnouts and sale of parcels				9,039
Gains from condemnation awards, earnouts and sale of parcels				6,652
Aggregate net proceeds from property sales and additional transactions	200,645	160,303		200,645	160,303
Aggregate gains from sale of investment properties	$ 23,170	$ 22,849		$ 23,170	$ 22,849