Debt Of The Operating Partnership (Exchangeable Senior Debentures) (Details) (USD $) In Thousands, unless otherwise specified					9 Months Ended		9 Months Ended			12 Months Ended
	Sep. 30, 2011	Dec. 31, 2010	Sep. 30, 2011 Exchangeable Senior Debentures [Member]	Dec. 31, 2010 Exchangeable Senior Debentures [Member]	Sep. 30, 2011 Exchangeable Senior Debentures [Member] 5.50% Exchangeable Senior Debentures Due 2029 [Member]	Dec. 31, 2010 Exchangeable Senior Debentures [Member] 5.50% Exchangeable Senior Debentures Due 2029 [Member]	Sep. 30, 2011 Exchangeable Senior Debentures [Member] 4.125% Exchangeable Senior Debentures Due 2026 [Member]	Dec. 31, 2010 Exchangeable Senior Debentures [Member] 4.125% Exchangeable Senior Debentures Due 2026 [Member]	Dec. 31, 2010 4.125% Exchangeable Senior Debentures Due 2026 [Member]	Dec. 31, 2010 5.50% Exchangeable Senior Debentures Due 2029 [Member]	Apr. 15, 2024 5.50% Exchangeable Senior Debentures Due 2029 [Member]	Apr. 15, 2019 5.50% Exchangeable Senior Debentures Due 2029 [Member]	Apr. 15, 2014 5.50% Exchangeable Senior Debentures Due 2029 [Member]	Sep. 30, 2011 5.50% Exchangeable Senior Debentures Due 2029 [Member]
Debt of the Operating Partnership [Line Items]
Interest Rate at September 30, 2011					5.50%		4.125%							5.50%
Maturity Date					Apr. 15, 2029		Aug. 15, 2026
Unamortized discounts	$ (9,172)			$ (1,456)					$ (1,456)
Exchangeable senior debentures net of discount	$ 266,400	$ 353,702	$ 266,400	$ 353,702	$ 266,400	$ 266,400		$ 88,758
Purchase price/Redemption price percentage of debenture principal										100
Dates which the holders of may require the Operating Partnership to repurchase the debentures											April 15, 2024	April 15, 2019	April 15, 2014
Earliest date which The Company may repurchase debentures					April 18, 2014		August 18, 2011