Investment in Partially Owned Entities (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Liabilities and Equity
Carrying value of investments in unconsolidated entities	$ 306,442		$ 306,442		$ 253,799
Company’s share of:
Net income, net of excess basis depreciation of $400 and $257	3,000	291	11,044	2,807
Unconsolidated Entities [Member]
Schedule of Equity Method Investments [Line Items]
Accumulated Depreciation of Investments over Book Value	1,072		1,072		1,714
Assets
Real estate assets, net of accumulated depreciation	1,696,988		1,696,988		1,437,268
Other assets	306,157		306,157		222,096
Total Assets	2,003,145		2,003,145		1,659,364
Liabilities and Equity
Mortgage debt	1,245,144		1,245,144		1,062,086
Other liabilities	94,941		94,941		89,573
Equity	663,060		663,060		507,705
Total Liabilities and Equity	2,003,145		2,003,145		1,659,364
Company’s share of equity	321,573		321,573		252,994
Net excess of cost of investments over the net book value of underlying net assets (net of accumulated depreciation of $1,072 and $1,714, respectively)	(15,131)		(15,131)		805
Carrying value of investments in unconsolidated entities	306,442		306,442		253,799
Statements of Operations:
Revenues			168,863	156,308
Expenses:
Interest expense and loan cost amortization			38,344	44,938
Depreciation and amortization			51,438	60,048
Operating expenses, ground rent and general and administrative expenses			55,121	52,157
Impairment			0	553
Total expenses			144,903	157,696
Net gain (loss) before gain on sale of real estate			23,960	(1,388)
Gain on sale of real estate			0	9,270
Net income (loss)			23,960	7,882
Company’s share of:
Depreciation			$ 400	$ 257