Equity (Details Textual) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) shares $ / shares	Dec. 31, 2014 $ / shares shares
Common Stock Disclosures [Abstract]
Common shares of beneficial interest, shares authorized	500,000,000	500,000,000
Common shares of beneficial interest, par value (usd per share) | $ / shares	$ 0.01	$ 0.01
Preferred Stock Disclosures [Abstract]
Preferred shares of beneficial interest, shares authorized	100,000,000	100,000,000
Preferred shares of beneficial interest, par value (usd per share) | $ / shares	$ 0.01	$ 0.01
Preferred Stock, Shares Outstanding	14,000,000	14,000,000
Preferred shares of beneficial interest, redemption price per share (usd per share) | $ / shares	$ 25.00
LTIP Units Disclosures [Abstract]
Operating Partnership outstanding	236,351	236,351
LTIP units, vested	9,469
6.50% Series C [Member]
Preferred Stock Disclosures [Abstract]
Preferred Stock, Shares Outstanding	5,000,000	5,000,000
Preferred Stock, Dividend Rate, Percentage	6.50%	6.50%
Share cap on each preferred shares	2.0325
7.875% Series A [Member]
Preferred Stock Disclosures [Abstract]
Preferred Stock, Shares Outstanding	5,600,000	5,600,000
Preferred Stock, Dividend Rate, Percentage	7.875%	7.875%
Share cap on each preferred shares	2.3234
8.00% Series B [Member]
Preferred Stock Disclosures [Abstract]
Preferred Stock, Shares Outstanding	3,400,000	3,400,000
Preferred Stock, Dividend Rate, Percentage	8.00%	8.00%
Share cap on each preferred shares	3.4483
ATMProgram [Member]
Common Stock Disclosures [Abstract]
Mar 2014 Shelf Registration Stmt Maximum Amount | $	$ 175.0
Sept 2012 Shelf Registration Stmt Maximum Amount | $	170.0
Amount Available under ATM Program | $	$ 159.8