Investments in Unconsolidated Joint Ventures (Schedules of Combined Financial Statements for the Unconsolidated Joint Ventures)(Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Assets
Commercial real estate property, net	$ 12,828,941		$ 14,620,896
Other assets	1,055,267		850,939
Liabilities and members' equity
Mortgages and other loans payable, net	5,585,171		6,881,920
Other liabilities	247,950		168,477
Company's investments in unconsolidated joint ventures	1,146,085		1,203,858
Combined statements of income for the unconsolidated joint ventures
Operating expenses	79,520	$ 76,777
Ground rent	8,308	8,188
Real estate taxes	61,674	55,723
Interest expense, net of interest income	94,672	75,807
Amortization of deferred financing costs	7,932	6,615
Transaction related costs	1,279	1,143
Depreciation and amortization	179,308	108,337
Total expenses	456,725	358,054
Company's equity in net income from unconsolidated joint ventures	10,096	4,030
Joint venture
Assets
Commercial real estate property, net	5,998,692		6,122,468
Debt and preferred equity investments, net	284,014		145,878
Other assets	673,317		715,840
Total assets	6,956,023		6,984,186
Liabilities and members' equity
Mortgages and other loans payable, net	4,319,655		4,266,548
Other liabilities	523,359		523,160
Members' equity	2,113,009		2,194,478
Total liabilities and members' equity	6,956,023		$ 6,984,186
Combined statements of income for the unconsolidated joint ventures
Total revenues	162,512	128,916
Operating expenses	27,254	25,486
Ground rent	3,211	2,592
Real estate taxes	24,210	19,376
Interest expense, net of interest income	49,736	44,007
Amortization of deferred financing costs	3,236	3,010
Transaction related costs	0	8
Depreciation and amortization	37,851	32,984
Total expenses	145,498	127,463
Loss on early extinguishment of debt	(1,606)	(833)
Net income before gain on sale	15,408	620
Company's equity in net income from unconsolidated joint ventures	10,096	4,030
Joint venture
Investment in Unconsolidated Joint Ventures
Management fees, base revenue	$ 4,500	$ 2,800