Investments in Unconsolidated Joint Ventures (Schedules of Combined Financial Statements for the Unconsolidated Joint Ventures)(Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
Assets
Commercial real estate property, net	$ 9,504,720		$ 9,504,720		$ 10,478,638
Cash and cash equivalents	270,965	$ 276,226	270,965	$ 276,226	279,443	$ 255,399
Tenant and other receivables, related party receivables, and deferred rents receivable, net of allowance	50,946		50,946		53,772
Other assets	360,096		360,096		614,067
Liabilities and members' equity
Mortgages and other loans payable, net	3,813,976		3,813,976		4,073,830
Deferred revenue/gain	229,692		229,692		217,955
Other liabilities	195,940		195,940		206,238
Company's investments in unconsolidated joint ventures	2,219,371		2,219,371		1,890,186
Combined statements of income for the unconsolidated joint ventures
Operating expenses	70,852	75,324	145,358	154,844
Ground rent	8,308	8,307	16,616	16,615
Real estate taxes	60,945	62,124	122,013	123,798
Interest expense, net of interest income	64,856	89,089	130,478	183,761
Amortization of deferred financing costs	3,432	7,433	8,193	15,365
Transaction related costs	46	2,115	179	3,394
Depreciation and amortization	133,054	425,042	227,188	604,350
Total expenses	365,749	693,918	698,424	1,150,643
Company's equity in net income from unconsolidated joint ventures	3,412	5,841	10,026	15,937
Joint venture
Investment in Unconsolidated Joint Ventures
Management fees, base revenue	12,600	2,000	25,200	2,500
Assets
Commercial real estate property, net	9,868,906		9,868,906		9,131,717
Cash and cash equivalents	316,941		316,941		328,455
Tenant and other receivables, related party receivables, and deferred rents receivable, net of allowance	261,222		261,222		232,778
Debt and preferred equity investments, net	201,299		201,299		336,164
Other assets	631,543		631,543		683,481
Total assets	11,279,911		11,279,911		10,712,595
Liabilities and members' equity
Mortgages and other loans payable, net	6,689,487		6,689,487		6,453,966
Deferred revenue/gain	340,253		340,253		356,414
Other liabilities	395,662		395,662		391,500
Members' equity	3,854,509		3,854,509		3,510,715
Total liabilities and members' equity	11,279,911		11,279,911		$ 10,712,595
Combined statements of income for the unconsolidated joint ventures
Total revenues	210,590	151,575	427,109	314,087
Operating expenses	39,147	27,166	77,941	54,420
Ground rent	4,179	3,715	8,430	6,926
Real estate taxes	35,170	24,332	70,109	48,542
Interest expense, net of interest income	59,702	46,351	115,030	96,087
Amortization of deferred financing costs	7,458	7,276	13,963	10,512
Transaction related costs	56	0	146	0
Depreciation and amortization	65,944	37,294	137,109	75,145
Total expenses	211,656	146,134	422,728	291,632
Loss on early extinguishment of debt	0	0	0	(1,606)
Net (loss) income before gain on sale	(1,066)	5,441	4,381	20,849
Company's equity in net income from unconsolidated joint ventures	$ 3,412	$ 5,841	$ 10,026	$ 15,937