Beneficiaries Equity of The Parent Company (DetailsTextuals) (USD $)	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Oct. 19, 2011	Oct. 05, 2011	May 02, 2006
Class of Stock [Line Items]
Dividends paid for preferred shares	$ 5,994,000	$ 5,994,000
Beneficiaries Equity of The Parent Company (Textuals) [Abstract]
Redeemable limited partnership units excluded from the diluted earnings per share computations	9,809,759	9,920,220
Distribution Declared per common partnership unit			$ 0.15
Amount of dividend declared				20,500,000
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
Issuance of Common Shares of Beneficial Interest	8,272,000	66,927,000
Number of shares sold by the company	6,421,553
Remaining shares available for sales	8,578,447
Common partnership units issued to the parent company	679,285
Common shares capacity restored					3,500,000
Additional shares Expected to be purchased under program	500,000
7.50% Series C Preferred Shares [Member]
Class of Stock [Line Items]
Dividends paid for preferred shares	900,000
Percentage of Preferential return	7.50%
7.375% Series D Preferred Shares [Member]
Class of Stock [Line Items]
Dividends paid for preferred shares	$ 1,100,000
Percentage of Preferential return	7.375%