Debt Of The Operating Partnership (Exchangeable Senior Debentures) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012		Dec. 31, 2011
Debt of the Operating Partnership [Line Items]
Interest rate	4.125%
Unamortized discounts	$ (8,681)
Exchangeable senior debentures net of discount	266,400		266,400
4.125% Exchangeable Senior Debentures Due 2026 [Member]
Debt of the Operating Partnership [Line Items]
Purchase price/Redemption price percentage of debenture principal	100
5.50% Exchangeable Senior Debentures Due 2029 [Member]
Debt of the Operating Partnership [Line Items]
Purchase price/Redemption price percentage of debenture principal	100
Exchangeable Senior Debentures [Member]
Debt of the Operating Partnership [Line Items]
Exchangeable senior debentures net of discount	266,400		266,400
Exchangeable Senior Debentures [Member] | 5.50% Exchangeable Senior Debentures Due 2029 [Member]
Debt of the Operating Partnership [Line Items]
Interest rate	5.50%
Maturity Date	Apr. 15, 2029	[1]
Exchangeable senior debentures net of discount	$ 266,400		$ 266,400

[1] The holders of the debentures have the right to require the Operating Partnership to repurchase the debentures in cash in whole or in part for a price of 100% of the principal amount plus accrued and unpaid interest on each of April 15, 2014, April 15, 2019 and April 15, 2024. We have the right to redeem the debentures in cash for a price of 100% of the principal amount plus accrued and unpaid interest commencing on April 18, 2014.