Common Shares Of Beneficial Interest (Details) (USD $)	12 Months Ended			3 Months Ended		2 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Quarterly Rate Per Share [Member]	Dec. 31, 2012 Quarterly Rate Per Share [Member]	Feb. 26, 2014 Quarterly Rate Per Share [Member] Subsequent Event [Member]
Class of Stock [Line Items]
Common shares of beneficial interest, dividend per share	$ 1.22	$ 1.16	$ 1.10	$ 0.305	$ 0.290	$ 0.325