Properties, net (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Properties
Operating properties, net	$ 2,713,579	$ 2,597,666
Operating properties, net
Properties
Less: accumulated depreciation	(612,369)	(555,975)
Operating properties, net | Land
Properties
Gross	436,565	427,766
Operating properties, net | Buildings and improvements
Properties
Gross	$ 2,889,383	$ 2,725,875