Beneficiaries Equity of The Parent Company (DetailsTextuals) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended						12 Months Ended		12 Months Ended			0 Months Ended	12 Months Ended	0 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	May 02, 2006	Dec. 11, 2012 Dividend Declared [Member]	Dec. 11, 2012 Dividend Paid	Dec. 31, 2012 Series E Preferred Stock [Member]	Apr. 11, 2012 Series E Preferred Stock [Member]	Dec. 31, 2012 Class A Units [Member]	Dec. 31, 2011 Class A Units [Member]	Dec. 31, 2010 Class A Units [Member]	May 03, 2012 7.50% Series C Preferred Shares	Dec. 31, 2012 7.50% Series C Preferred Shares	Dec. 28, 2012 Series D Preferred Stock [Member]	Dec. 31, 2012 Series D Preferred Stock [Member]	Dec. 31, 2012 Offering Program [Member]	Dec. 31, 2011 Offering Program [Member]	Dec. 31, 2012 Series D Preferred Stock [Member]	Dec. 31, 2011 Series D Preferred Stock [Member]	Dec. 31, 2012 6.90% Series E Preferred Stock [Member]	Dec. 31, 2012 Series C Preferred Stock [Member]	Dec. 31, 2011 Series C Preferred Stock [Member]
Class of Stock [Line Items]
Stock Redeemed or Called During Period, Value	$ (103,448)											$ 50,000		$ 57,500						$ (43)
Stub period dividend accrual														(848)
Net Proceeds from Issuance of Preferred Stock and Preference Stock	96,237	0	0				96,300
Stock Redeemed or Called During Period, Shares												2,000,000		2,300,000						(4,300,000)
Beneficiaries Equity of The Parent Company (Textuals) [Abstract]
Antidilutive securities excluded from computation of earnings per share									1,845,737	2,698,647	9,902,752
Preferred Stock, Shares Issued								4,000,000										0	2,300,000	4,000,000	0	2,000,000
Distribution Declared per common partnership unit					$ 0.15
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																$ 12.50	$ 12.18
Issuance of Common Shares of Beneficial Interest		8,272	71,981														8,000
Common partnership units issued to the parent company related to redemption																	679,285
Number of shares sold by the company																6,421,553
Remaining shares available for sales																8,578,447
Common shares capacity restored				3,500,000
Additional shares Expected to be purchased under program	500,000
Dividends paid for preferred shares	10,405	7,992	7,992				1,700					200
Percentage of Preferential return							6.90%											0.00%	7.375%	6.90%	0.00%	7.50%
Preferred Stock, Liquidation Preference Per Share							$ 25	$ 25
Preferred Stock, per share per annum							$ 1.725
Dividends Payable, Amount	23,652	23,895				21,600
Redemption Premium	$ 4,052	$ 0	$ 0										$ (2,100)		$ (2,000)