Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 28	$ 71
Debt Instrument, Unamortized Premium	2,498	0
Preferred shares of beneficial interest, liquidation preference value	$ 225,000	$ 225,000
Preferred shares of beneficial interest, par value	$ 0.01	$ 0.01
Preferred shares of beneficial interest, shares authorized	100,000,000	100,000,000
Preferred shares of beneficial interest, shares issued	9,000,000	9,000,000
Preferred shares of beneficial interest, shares outstanding	9,000,000	9,000,000
Common shares of beneficial interest, par value	$ 0.01	$ 0.01
Common shares of beneficial interest, shares authorized	500,000,000	500,000,000
Common shares of beneficial interest, shares issued	60,955,090	50,769,024
Common shares of beneficial interest, shares outstanding	60,955,090	50,769,024