Debt of the Operating Partnership (Other Secured Loans) (Details) (USD $) In Thousands	6 Months Ended
	Jun. 30, 2011		Dec. 31, 2010
Other secured loan	$ 10,500		$ 10,500
Total indebtedness	3,067,577		2,806,954
Other Secured Loans [Member]
Other secured loan	10,500		10,500
Other Secured Loans [Member] | 800 Central Expressway Mezzanine [Member]
Variable Rate Basis	1-month LIBOR + 8.50%
Maturity Date	Jun. 09, 2013	[1]
Other secured loan	$ 10,500	[1]	$ 10,500	[1]

[1] The respective borrower's assets and credit are not available to satisfy the debts and other obligations of affiliates or any other person.