Preferred Shares Of Beneficial Interest (Details) (USD $)	12 Months Ended			3 Months Ended	12 Months Ended				12 Months Ended	1 Months Ended	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Jun. 30, 2013 6.5% Series F Preferred Shares [Member]	Dec. 31, 2013 6.5% Series F Preferred Shares [Member]	Dec. 31, 2012 6.5% Series F Preferred Shares [Member]	Jun. 06, 2008 6.5% Series F Preferred Shares [Member]	Jan. 30, 2007 6.5% Series F Preferred Shares [Member]	Dec. 31, 2013 6.5% Series F Preferred Shares [Member] Preferred Shares Issued At Discount [Member]	Mar. 31, 2013 6.75% Series D Preferred Shares [Member]	Dec. 31, 2013 6.75% Series D Preferred Shares [Member]	Dec. 31, 2012 6.75% Series D Preferred Shares [Member]	Apr. 30, 2003 6.75% Series D Preferred Shares [Member]
Class of Stock [Line Items]
Preferred shares of beneficial interest, value					$ 2,000	$ 4,000	$ 150,000,000	$ 200,000,000			$ 0	$ 3,000	$ 75,000,000
Preferred shares of beneficial interest, depositary shares, conversion basis					0.01								0.0333
Preferred shares of beneficial interest, redemption price per depositary share					$ 25						$ 25
Preferred shares of beneficial interest, dividend percentage					6.50%	6.50%				6.75%	6.75%	6.75%
Preferred shares of beneficial interest, liquidation value per share					$ 2,500						$ 750
Preferred shares of beneficial interest, effective dividend yield percentage					8.25%				8.25%
Preferred Shares of beneficial interest, redemption value paid					200,000,000					75,000,000	75,000,000
Preferred shares of beneficial interest, liquidation preference					150,000,000	350,000,000			64,300,000		0	75,000,000
Preferred shares of beneficial interest, redemption date					Jun. 05, 2013						Mar. 18, 2013
Redemption costs of preferred shares	$ 17,944,000	$ 2,500,000	$ 0	$ 15,700,000	$ 15,700,000						$ 2,200,000