Investments in Unconsolidated Joint Ventures (Schedules of Combined Financial Statements for the Unconsolidated Joint Ventures)(Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015	Dec. 31, 2014
Assets
Commercial real estate property, net	$ 10,418,719		$ 10,418,719		$ 14,620,896
Cash and cash equivalents	405,896	$ 244,360	405,896	$ 244,360	255,399	$ 281,409
Tenant and other receivables, related party receivables, and deferred rents receivable, net of allowance	55,976		55,976		63,491
Other assets	620,838		620,838		850,939
Liabilities and members' equity
Mortgages and other loans payable, net	3,954,155		3,954,155		6,881,920
Deferred revenue/gain	237,548		237,548		399,102
Other liabilities	211,513		211,513		168,477
Company's investments in unconsolidated joint ventures	1,860,912		1,860,912		1,203,858
Combined statements of income for the unconsolidated joint ventures
Operating expenses	79,425	78,648	234,269	225,539
Ground rent	8,338	8,252	24,953	24,526
Real estate taxes	64,133	61,009	187,931	173,018
Interest expense, net of interest income	72,565	84,141	256,326	235,694
Amortization of deferred financing costs	4,815	7,160	20,180	19,727
Transaction related costs	2,593	5,829	5,987	10,039
Depreciation and amortization	112,665	146,185	717,015	454,087
Total expenses	369,992	414,699	1,520,635	1,214,769
Company's equity in net (loss) income from unconsolidated joint ventures	(3,968)	3,627	11,969	10,651
Joint venture
Investment in Unconsolidated Joint Ventures
Management fees, base revenue	2,000	1,900	4,500	6,800
Assets
Commercial real estate property, net	8,927,385		8,927,385		6,122,468
Cash and cash equivalents	320,318		320,318		258,564
Tenant and other receivables, related party receivables, and deferred rents receivable, net of allowance	227,937		227,937		208,802
Debt and preferred equity investments, net	332,506		332,506		145,878
Other assets	670,665		670,665		248,474
Total assets	10,478,811		10,478,811		6,984,186
Liabilities and members' equity
Mortgages and other loans payable, net	6,332,506		6,332,506		4,266,548
Deferred revenue/gain	367,873		367,873		209,095
Other liabilities	374,198		374,198		314,065
Members' equity	3,404,234		3,404,234		2,194,478
Total liabilities and members' equity	10,478,811		10,478,811		$ 6,984,186
Combined statements of income for the unconsolidated joint ventures
Total revenues	184,221	150,638	498,308	423,089
Operating expenses	34,727	27,647	89,147	79,478
Ground rent	3,744	4,677	10,670	9,841
Real estate taxes	30,814	23,494	79,356	65,205
Interest expense, net of interest income	51,789	51,430	147,876	147,152
Amortization of deferred financing costs	7,155	3,473	17,667	9,628
Transaction related costs	5,359	604	5,359	615
Depreciation and amortization	56,890	38,144	132,035	109,022
Total expenses	190,478	149,469	482,110	420,941
Loss on early extinguishment of debt	0	(248)	(1,606)	(1,081)
Net (loss) income before gain on sale	(6,257)	921	14,592	1,067
Company's equity in net (loss) income from unconsolidated joint ventures	$ (3,968)	$ 3,627	$ 11,969	$ 10,651