Investment in Partially Owned Entities (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Liabilities and Equity
Carrying value of investments in unconsolidated entities	$ 253,308		$ 253,799
Company’s share of:
Net income (loss), net of excess basis depreciation of $33 and $85	(974)	(419)
Unconsolidated Entities [Member]
Schedule of Equity Method Investments [Line Items]
Accumulated Depreciation of Investments over Book Value	1,747		1,714
Assets:
Real estate assets, net of accumulated depreciation	1,394,845		1,437,268
Other assets	225,904		222,096
Total Assets	1,620,749		1,659,364
Liabilities and Equity
Mortgage debt	1,050,458		1,062,086
Other liabilities	83,612		89,573
Equity	486,679		507,705
Total Liabilities and Equity	1,620,749		1,659,364
Company’s share of equity	252,538		252,994
Net excess of cost of investments over the net book value of underlying net assets (net of accumulated depreciation of $1,747 and $1,714, respectively)	770		805
Carrying value of investments in unconsolidated entities	253,308		253,799
Statements of Operations:
Revenues	43,237	60,261
Expenses:
Interest expense and loan cost amortization	12,121	17,589
Depreciation and amortization	15,330	25,371
Operating expenses, ground rent and general and administrative expenses	16,547	19,796
Total expenses	43,998	62,756
Net income (loss)	(761)	(2,495)
Company’s share of:
Depreciation	$ 33	$ 85