Beneficiaries Equity of The Parent Company (DetailsTextuals) (USD $)	12 Months Ended				0 Months Ended	12 Months Ended				12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	May 02, 2006	Dec. 23, 2011 Class F (2010) Units	Dec. 31, 2011 7.50% Series C Preferred Shares	Dec. 31, 2011 Series D Preferred Stock [Member]	Jan. 19, 2012 Dividend Declared	Jan. 05, 2012 Dividend Paid	Dec. 31, 2011 Series C Preferred Stock [Member]	Dec. 31, 2010 Series C Preferred Stock [Member]	Dec. 31, 2003 Series C Preferred Stock [Member]	Dec. 31, 2011 Series D Preferred Stock [Member]	Dec. 31, 2010 Series D Preferred Stock [Member]	Dec. 31, 2004 Series D Preferred Stock [Member]	Dec. 31, 2011 Subsidiaries [Member]	Dec. 13, 2011 Subsidiaries [Member]	Aug. 05, 2010 Subsidiaries [Member] Class F (2010) Units
Class of Stock [Line Items]
Dividends paid for preferred shares	$ 7,992,000	$ 7,992,000	$ 7,992,000			$ 900,000	$ 1,100,000
Percentage of Preferential return						7.50%	7.375%			7.50%	7.50%	7.50%	7.375%	7.375%	7.375%
Proceeds from issuance of redeemable preferred shares (in dollars)												48,100,000			55,500,000
Preferred shares, shares issued										2,000,000	2,000,000	2,000,000	2,300,000	2,300,000	2,300,000
Preferred shares, redemption price (in dollars per share)										$ 25			$ 25.00
Beneficiaries Equity of The Parent Company (Textuals) [Abstract]
Antidilutive securities excluded from computation of earnings per share	2,698,647	9,902,752	2,809,108
Partnership units issued for acquisition																		7,111,112
Distribution Declared per common partnership unit								$ 0.15									$ 0.15
Amount of dividend declared									21,500,000
Shares authorized for Equity Offering Program	15,000,000
Maximum percentage of Gross sale price per share, compensation to sales agents	2.00%
Issuance of Common Shares of Beneficial Interest, shares	679,285
Average sales price per share	$ 12.18
Proceeds from Contributions from Parent	8,000,000
Issuance of Common Shares of Beneficial Interest	$ 8,272,000	$ 71,981,000	$ 242,323,000
Remaining shares available for sales	8,578,447
Common partnership units issued to the parent company related to redemption					7,111,112											679,285
Common Partnership Units Issued	6,421,553
Common shares capacity restored				3,500,000
Additional shares Expected to be purchased under program	500,000