Real Estate Fund Investments (Narrative) (Details)					3 Months Ended		9 Months Ended		12 Months Ended
	Apr. 19, 2018 USD ($) extension	Feb. 16, 2018 USD ($)	Jan. 17, 2018 USD ($)	Mar. 01, 2011 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) investment	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($) investment
Investment Holdings
Gain (loss) on sale of properties							$ 0	$ 3,797,000
Loss from real estate fund investments					$ (190,000)	$ (6,308,000)	(37,973,000)	(1,649,000)
Income (loss) from partially owned entities					7,206,000	(41,801,000)	6,059,000	5,578,000
Number of investments held by fund | investment									5
Aggregate fair value of Real Estate Fund investments (in US Dollars)					$ 369,767,000		$ 369,767,000		$ 354,804,000
Crowne Plaza Times Square Hotel Joint Venture
Investment Holdings
Refinancing	$ 255,000,000
Vornado Capital Partners Real Estate Fund
Investment Holdings
Equity method ownership percentage					25.00%		25.00%
Term of the Fund, years							8 years
Investment period for commitments of the Fund, years							3 years
Investment fund expiration date							2013-07
Vornado Realty Trust
Investment Holdings
Unfunded commitments of fund					$ 16,119,000		$ 16,119,000
Real estate fund investments
Investment Holdings
Real estate transfer tax					0	0	10,630,000	0
Loss from real estate fund investments					(190,000)	$ (6,308,000)	$ (37,973,000)	$ (1,649,000)
Number of investments held by fund | investment							4
Unfunded commitments of fund					$ 50,494,000		$ 50,494,000
Eleven East 68th Street
Investment Holdings
Proceeds from the sale of real estate			$ 82,000,000
Gain (loss) on sale of properties			$ 46,259,000
One Park Avenue
Investment Holdings
Payments to acquire real estate				$ 394,000,000
Real estate transfer tax				$ 3,000,000			$ 4,978,000
State and Local Jurisdiction | One Park Avenue
Investment Holdings
Additional real estate transfer tax		$ 9,491,000
Interest on real estate transfer tax		6,764,000
Real estate transfer tax and interest		15,608,000
Loss from real estate fund investments		10,630,000
Income (loss) from partially owned entities		$ 4,978,000
Joint Venture | Crowne Plaza Times Square Hotel Joint Venture
Investment Holdings
Equity method ownership percentage					57.10%		57.10%
Joint Venture | Crowne Plaza Times Square Hotel Joint Venture | Crowne Plaza Time Square Hotel
Investment Holdings
Ownership percentage by noncontrolling owners					24.70%		24.70%
Joint Venture | Vornado Capital Partners Real Estate Fund
Investment Holdings
Equity method ownership percentage				64.70%
Joint Venture | Vornado Realty Trust
Investment Holdings
Equity method ownership percentage				30.30%
Joint Venture | Third Party
Investment Holdings
Equity method ownership percentage				5.00%
Loans Due May 2020 | Crowne Plaza Times Square Hotel Joint Venture
Investment Holdings
Debt instrument, interest rate, stated percentage					5.66%		5.66%
Loans Due December 2018 | Crowne Plaza Times Square Hotel Joint Venture
Investment Holdings
Refinancing	$ 310,000,000
LIBOR | Loans Due May 2020 | Crowne Plaza Times Square Hotel Joint Venture
Investment Holdings
Spread Over LIBOR (in percentage)	3.51%
Number of extensions | extension	3
Length of extension available	1 year
LIBOR | Loans Due December 2018 | Crowne Plaza Times Square Hotel Joint Venture
Investment Holdings
Spread Over LIBOR (in percentage)	2.80%
LIBOR | Interest Rate Cap | Loans Due May 2020 | Crowne Plaza Times Square Hotel Joint Venture
Investment Holdings
Spread Over LIBOR (in percentage)	4.00%