Investment in Real Estate (Details 2) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Summary of net non-cash impairment charges
Impairment of Real Estate	$ 2,661	$ (194,552)	$ (6,934)
Operating Properties - Held for Sale and Sold Assets [Member]
Summary of net non-cash impairment charges
Impairment of Real Estate	(6,146)	(81,648)	(1,317)
Impairment - Discontinued Operations [Member]
Summary of net non-cash impairment charges
Impairment of Real Estate	(6,146)	(81,648)	(1,317)
Land Parcels - Held for Sale and Sold Assets [Member]
Summary of net non-cash impairment charges
Impairment of Real Estate	5,879	(8,275)
Operating Properties - Held for Use [Member]
Summary of net non-cash impairment charges
Impairment of Real Estate	1,687	(90,204)	(5,617)
Land Parcels - Held for Use [Member]
Summary of net non-cash impairment charges
Impairment of Real Estate	1,241	(14,425)
Impairment - Continuing Operations [Member]
Summary of net non-cash impairment charges
Impairment of Real Estate	$ 8,807	$ (112,904)	$ (5,617)