Co-Venture Arrangement: (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended			1 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Sep. 30, 2009 Freehold Raceway Mall and Chandler Fashion Center
Co-Venture Arrangement:
Interest sold to third party (as a percent)				49.90%
Number of common shares available for purchase under warrant				935,358
Exercise price of stock warrants (in dollars per share)				$ 46.68
Cash proceeds for sale of interest in property	$ 6,059	$ 23,180		$ 174,650
Proceeds attributed to the warrants				6,496
Co-venture obligation	$ 89,360		$ 92,215	$ 168,154