Investment in Joint Venture (Details Textual) (USD $)	Sep. 30, 2012 properties	Dec. 31, 2011	Jul. 29, 2011
Investment in Joint Venture (Textual) [Abstract]
Number of properties owned	24
Transaction Values Of Investment In Joint Venture			$ 908,000,000
Preferred capital	90,000	90,000
Manhattan Collection Joint Venture [Member]
Investment in Joint Venture (Textual) [Abstract]
Equity interest issued in a joint venture	49.00%		49.00%
Number of properties owned	6		6
Total assets of joint venture	540,900,000
Amount existing first mortgage and mezzanine debt	560,800,000
Preferred capital	$ 76,600,000