Investment in Unconsolidated Joint Ventures (Details 3) (USD $) In Thousands, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013	Sep. 30, 2014		Sep. 30, 2013	Dec. 31, 2013
Assets
Commercial real estate property, net	$ 12,119,615			$ 12,119,615			$ 10,687,540
Other assets	729,538			729,538			750,123
Liabilities and members' equity
Mortgages and other loans payable	6,338,184	[1]		6,338,184	[1]		4,860,578	[1]
Company's investments in unconsolidated joint ventures	996,842			996,842			1,113,218
Combined statements of income for the unconsolidated joint ventures
Operating expenses	72,111		72,784	211,118		205,921
Ground rent	8,088		7,930	24,161		23,988
Real estate taxes	55,548		51,529	159,702		149,857
Interest expense, net of interest income	82,376		78,226	236,424		232,862
Amortization of deferred financing costs	6,679		4,121	15,737		12,404
Transaction related costs, net of recoveries	2,383		(2,368)	6,554		717
Depreciation and amortization	94,443		84,162	274,337		238,666
Total expenses	344,277		317,253	997,811		927,865
Company's equity in net income from unconsolidated joint ventures	6,034		2,939	20,781		4,251
Joint Venture
Assets
Commercial real estate property, net	4,850,149			4,850,149			6,846,021
Other assets	746,234			746,234			827,282
Total assets	5,596,383			5,596,383			7,673,303
Liabilities and members' equity
Mortgages and other loans payable	3,498,755			3,498,755			5,066,710
Other liabilities	474,427			474,427			596,960
Members' equity	1,623,201			1,623,201			2,009,633
Total liabilities and members' equity	5,596,383			5,596,383			7,673,303
Company's investments in unconsolidated joint ventures	996,842			996,842			1,113,218
Combined statements of income for the unconsolidated joint ventures
Total revenues	114,831		156,571	406,464		462,776
Operating expenses	18,530		29,211	63,575		86,027
Ground rent	2,638		657	7,295		1,972
Real estate taxes	15,867		19,105	48,209		53,368
Interest expense, net of interest income	40,885		56,169	137,949		169,137
Amortization of deferred financing costs	2,837		2,869	9,496		12,454
Transaction related costs, net of recoveries	501		0	565		0
Depreciation and amortization	28,324		49,402	107,786		144,552
Total expenses	109,582		157,413	374,875		467,510
Loss on early extinguishment of debt	0		0	(6,743)		0
Net income (loss) before gain on sale	5,249		(842)	24,846		(4,734)
Company's equity in net income from unconsolidated joint ventures	$ 6,034		$ 2,939	$ 20,781		$ 4,251

[1] Includes mortgages related to 2 Herald Square and 180 Maiden, which are currently held for sale.