Properties, net (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Properties
Gross	$ 4,158,616	$ 4,014,336	$ 3,811,950	$ 3,859,960
Operating properties, net	2,920,529	2,751,488
Operating properties, net [Member]
Properties
Less: accumulated depreciation	(700,363)	(703,083)
Operating properties, net [Member] | Land [Member]
Properties
Gross	463,305	439,355
Operating properties, net [Member] | Buildings and improvements [Member]
Properties
Gross	$ 3,157,587	$ 3,015,216