Consolidated Statements of Shareholders' Equity (Parenthetical) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Dividends paid or accrued per Common Share of Beneficial Interest	$ 0.65	$ 0.65	$ 0.9125
Dividends paid or accrued per Series C Preferred Share	$ 1.43	$ 1.625	$ 0.406
Dividends paid or accrued per Series D Preferred Share	$ 0.212
Accumulated Distributions in Excess of Net Income [Member]
Dividends paid or accrued per Common Share of Beneficial Interest	$ 0.65	$ 0.65	$ 0.9125
Dividends paid or accrued per Series C Preferred Share	$ 1.43	$ 1.625	$ 0.406
Dividends paid or accrued per Series D Preferred Share	$ 0.212