Investments in Unconsolidated Joint Ventures (Schedules of Combined Financial Statements for the Unconsolidated Joint Ventures)(Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Assets
Commercial real estate property, net	$ 14,620,896	$ 12,163,976
Other assets	850,719	647,333
Liabilities and members' equity
Mortgages and other loans payable	6,992,504	5,586,709
Company's investments in unconsolidated joint ventures	1,203,858	1,172,020
Combined statements of income for the unconsolidated joint ventures
Operating expenses	301,624	282,283	$ 276,589
Ground rent	32,834	32,307	31,951
Real estate taxes	232,702	217,843	203,076
Interest expense, net of interest income	323,870	317,400	310,894
Amortization of deferred financing costs	27,348	22,377	15,855
Transaction related costs	11,430	8,707	3,985
Depreciation and amortization	560,887	371,610	324,461
Total expenses	1,585,568	1,345,015	1,253,003
Company's equity in net income from unconsolidated joint ventures	13,028	26,537	9,921
Joint venture
Assets
Commercial real estate property, net	6,122,468	5,275,632
Other assets	904,283	810,567
Total assets	7,026,751	6,086,199
Liabilities and members' equity
Mortgages and other loans payable	4,309,113	3,778,704
Other liabilities	523,160	485,572
Members' equity	2,194,478	1,821,923
Total liabilities and members' equity	7,026,751	6,086,199
Company's investments in unconsolidated joint ventures	1,203,858	1,172,020
Combined statements of income for the unconsolidated joint ventures
Total revenues	576,845	522,132	628,649
Operating expenses	106,613	82,436	114,633
Ground rent	14,083	9,898	2,863
Real estate taxes	89,734	64,217	71,755
Interest expense, net of interest income	199,126	178,743	225,765
Amortization of deferred financing costs	13,394	12,395	17,092
Transaction related costs	615	535	808
Depreciation and amortization	149,023	137,793	192,504
Total expenses	572,588	486,017	625,420
Loss on early extinguishment of debt	(1,089)	(6,743)	0
Net income before gain on sale	3,168	29,372	3,229
Company's equity in net income from unconsolidated joint ventures	13,028	26,537	9,921
Joint venture
Investment in Unconsolidated Joint Ventures
Management fees, base revenue	$ 6,900	$ 16,900	$ 4,700