Preferred Shares Of Beneficial Interest (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands		9 Months Ended	12 Months Ended
	May. 08, 2015	Sep. 30, 2015	Dec. 31, 2014
Class of Stock [Line Items]
Redemption of preferred shares		$ 150,000
Preferred stock value issued		$ 0	$ 2
6.5% Series F Preferred Shares [Member]
Class of Stock [Line Items]
Redemption of preferred shares	$ 150,000
Redemption costs of preferred shares	$ 9,700
Preferred stock value issued			$ 150,000
Redemption price per depository share (usd per share)			$ 25
Preferred shares dividend percentage		6.50%	6.50%
Liquidation value per share (usd per share)			$ 2,500
Liquidation preference value			$ 150,000
6.5% Series F Preferred Shares [Member] | Preferred Shares Issued At Discount [Member]
Class of Stock [Line Items]
Liquidation preference value			$ 64,300
Effective dividend yield on preferred shares			8.25%