Preferred Shares Of Beneficial Interest (Details) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended	12 Months Ended
	May. 08, 2015	Jun. 05, 2013	Jun. 30, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Class of Stock [Line Items]
Stock redeemed or called during period, value				$ 150,000		$ 275,000
Preferred shares of beneficial interest, value				0	$ 2
Preferred shares of beneficial interest, redemption value paid				150,000	0	275,000
Redemption costs of preferred shares				$ 9,687	0	$ 17,944
Series F Preferred Stock [Member]
Class of Stock [Line Items]
Stock redeemed or called during period, value	$ 150,000
Preferred stock dividends and other adjustments	$ 9,700		$ 9,700
Preferred shares of beneficial interest, value					$ 150,000
Preferred shares of beneficial interest, redemption price per depositary share (in dollars per share)					$ 25
Preferred shares of beneficial interest, dividend percentage				6.50%	6.50%
Preferred shares of beneficial interest, liquidation value per share (in dollars per share)					$ 2,500
Preferred shares of beneficial interest, liquidation preference					$ 150,000
Preferred shares of beneficial interest, redemption value paid		$ 200,000
Redemption costs of preferred shares		$ 15,700
Series F Preferred Stock [Member] | Preferred Stock Issued At Discount [Member]
Class of Stock [Line Items]
Preferred shares of beneficial interest, liquidation preference					$ 64,300
Preferred shares of beneficial interest, effective dividend yield percentage					8.25%