Debt Of The Operating Partnership (Other Secured Loan) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012		Dec. 31, 2011
Debt of the Operating Partnership [Line Items]
Other secured loan	$ 10,500		$ 10,500
Total indebtedness	3,271,848		2,940,210
Other Secured Loans [Member]
Debt of the Operating Partnership [Line Items]
Other secured loan	10,500		10,500
Other Secured Loans [Member] | 800 Central Expressway Mezzanine [Member]
Debt of the Operating Partnership [Line Items]
Variable Rate Basis	1-month LIBOR + 8.50%	[1],[2]
Maturity Date	Jun. 09, 2013	[3]
Other secured loan	$ 10,500	[3]	$ 10,500	[3]

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

[2] We have entered into interest rate swap or interest rate cap agreements as a cash flow hedge for interest generated by these US LIBOR, EURIBOR and GBP LIBOR based loans. See note [13] for further information.

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