Equity (Details Textual) (USD $)	9 Months Ended			0 Months Ended		9 Months Ended		12 Months Ended	9 Months Ended	12 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Apr. 12, 2013 6.50% Series C [Member]	Mar. 18, 2013 6.50% Series C [Member]	Sep. 30, 2013 6.50% Series C [Member]	Sep. 30, 2013 7.875% Series A [Member]	Dec. 31, 2012 7.875% Series A [Member]	Sep. 30, 2013 8.00% Series B [Member]	Dec. 31, 2012 8.00% Series B [Member]	Sep. 30, 2013 ATMProgram [Member]
Common Stock Disclosures [Abstract]
Common shares of beneficial interest, shares authorized	500,000,000		500,000,000
Common shares of beneficial interest, par value	$ 0.01		$ 0.01
Sept 2012 Shelf Registration Stmt Maximum Amount											$ 165,200,000
Preferred Stock Disclosures [Abstract]
Preferred shares of beneficial interest, shares authorized	100,000,000		100,000,000
Preferred shares of beneficial interest, par value	$ 0.01		$ 0.01
Issuance of shares, net of offering costs, Shares				400,000	3,600,000						171,893
Preferred Stock, Dividend Rate, Percentage						6.50%	7.875%	7.875%	8.00%	8.00%
Preferred shares issued, net of commissions (per share)				$ 25.00	$ 25.00
Preferred Stock, Shares Outstanding	13,000,000		9,000,000			4,000,000	5,600,000	5,600,000	3,400,000	3,400,000
Preferred shares of beneficial interest, redemption price per share	$ 25.00
Share cap on each preferred shares						2.0325	2.3234		3.4483
Stock Issued During Period, Value Per Share, New Issues											$ 28.09
Proceeds from Issuance of Common Stock	4,829,000	218,054,000									4,800,000
LTIP Units Disclosures [Abstract]
Operating Partnership outstanding	381,109		381,109
LTIP units, vested	9,470
Net proceeds from issuance of preferred shares				9,600,000	87,100,000
Sept 2012 Shelf Registration Stmt Maximum Amount											$ 170,000,000