Investment Properties (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Investment Properties
Land	$ 3,747,079	$ 3,736,882
Buildings and improvements	31,026,081	30,187,495
Total land, buildings and improvements	34,773,160	33,924,377
Furniture, fixtures and equipment	353,184	328,144
Investment properties at cost	35,126,344	34,252,521
Less - accumulated depreciation	10,067,743	9,068,388
Investment properties, net	25,058,601	25,184,133
Construction in progress, included above	$ 364,542	$ 329,663