Investments in Unconsolidated Joint Ventures (Schedules of Combined Financial Statements for the Unconsolidated Joint Ventures)(Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Assets
Commercial real estate property, net	$ 10,387,209		$ 10,478,638
Cash and cash equivalents	468,035	$ 316,205	279,443	$ 255,399
Tenant and other receivables, related party receivables, and deferred rents receivable, net of allowance	52,197		53,772
Other assets	584,986		614,067
Liabilities and members' equity
Mortgages and other loans payable, net	4,167,270		4,073,830
Deferred revenue/gain	235,208		217,955
Other liabilities	162,964		206,238
Company's investments in unconsolidated joint ventures	1,861,077		1,890,186
Combined statements of income for the unconsolidated joint ventures
Operating expenses	74,506	79,520
Ground rent	8,308	8,308
Real estate taxes	61,068	61,674
Interest expense, net of interest income	65,622	94,672
Amortization of deferred financing costs	4,761	7,932
Transaction related costs	133	1,279
Depreciation and amortization	94,134	179,308
Total expenses	332,675	456,725
Company's equity in net income from unconsolidated joint ventures	6,614	10,096
Joint venture
Investment in Unconsolidated Joint Ventures
Management fees, base revenue	12,700	4,500
Assets
Commercial real estate property, net	8,734,099		9,131,717
Cash and cash equivalents	263,301		328,455
Tenant and other receivables, related party receivables, and deferred rents receivable, net of allowance	248,492		232,778
Debt and preferred equity investments, net	336,518		336,164
Other assets	694,384		683,481
Total assets	10,276,794		10,712,595
Liabilities and members' equity
Mortgages and other loans payable, net	6,498,732		6,453,966
Deferred revenue/gain	351,614		356,414
Other liabilities	367,980		391,500
Members' equity	3,058,468		3,510,715
Total liabilities and members' equity	10,276,794		$ 10,712,595
Combined statements of income for the unconsolidated joint ventures
Total revenues	216,521	162,512
Operating expenses	38,794	27,254
Ground rent	4,251	3,211
Real estate taxes	34,939	24,210
Interest expense, net of interest income	55,328	49,736
Amortization of deferred financing costs	6,505	3,236
Transaction related costs	89	0
Depreciation and amortization	71,164	37,851
Total expenses	211,070	145,498
Loss on early extinguishment of debt	0	(1,606)
Net income before gain on sale	5,451	15,408
Company's equity in net income from unconsolidated joint ventures	$ 6,614	$ 10,096