Investment in Partially Owned Entities (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Assets:
Real estate assets, net of accumulated depreciation	$ 16,914		$ 16,914
Liabilities and Equity
Carrying value of investments in unconsolidated entities	299,369		299,369		316,711
Company's share of:
Net income, net of excess basis depreciation of $171 and $104	2,936	7,733	2,517	5,435
Unconsolidated Entities [Member]
Assets:
Real estate assets, net of accumulated depreciation	2,024,894		2,024,894		1,949,035
Other assets	402,865		402,865		485,887
Total Assets	2,427,759		2,427,759		2,434,922
Liabilities and Equity
Mortgage debt	1,405,951		1,405,951		1,402,462
Other liabilities	111,029		111,029		94,361
Equity	910,779		910,779		938,094
Total Liabilities and Equity	2,427,759		2,427,759		2,434,917
Company's share of equity	290,306		290,306		307,684
Net excess of cost of investments over net book value of underlying net assets (net of accumulated depreciation of $1201 and $1,372, respectively)	9,063		9,063		9,027
Carrying value of investments in unconsolidated entities	299,369		299,369		316,711
Statements of Operations:
Revenues			121,072	140,425
Expenses:
Interest expense and loan cost amortization			(34,644)	(48,950)
Depreciation and amortization			(47,061)	(52,888)
Operating expenses, ground rent and general and administrative expenses			42,111	40,845
Impairment			(553)	0
Total expenses			124,369	142,683
Net loss before gain on sale of real estate			(3,297)	(2,258)
Gain on sale of real estate			6,663	12,147
Net income			3,366	9,889
Company's share of:
Net income, net of excess basis depreciation of $171 and $104			2,517	5,435
Depreciation and amortization (real estate related)	$ 21,436	$ 25,108	$ 21,436	$ 25,108