Stock-based Compensation (Out Performance Plans Narrative) (Details)		12 Months Ended
	Mar. 15, 2018 USD ($) component	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Full Value Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized (in shares) | shares		1,848,000
Full Value Awards | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized (in shares) | shares		6,000,000
Not Full Value Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized (in shares) | shares		12,000,000
Out Performance Plan
Out Performance Plan
Share-based compensation expense		$ 8,040,000	$ 7,558,000	$ 7,250,000
Amortized share based compensation		10,052,000
Out Performance Plan 2018
Out Performance Plan
Out of performance plan notional amount	$ 35,000,000	$ 35,000,000
Number of components of out performance plan | component	2
Percentage of notional amount granted		78.20%
Amount of basis points by which vornado underperforms the index, total	6.00%
Amount of basis points by which vornado underperforms the index	2.00%
Grant-date fair value		$ 10,300,000
OPP Units Earned, String		To be determined in 2021
Out Performance Plan 2017
Out Performance Plan
Out of performance plan notional amount		$ 35,000,000
Percentage of notional amount granted		86.60%
Grant-date fair value		$ 10,800,000
OPP Units Earned, String		To be determined in 2020
Out Performance Plan 2016
Out Performance Plan
Out of performance plan notional amount		$ 40,000,000
Percentage of notional amount granted		86.70%
Grant-date fair value		$ 11,800,000
OPP Units Earned, String		Not earned
Award Amortization Period		5 years
Absolute | Out Performance Plan 2018
Out Performance Plan
Duration of performance measurement period	3 years
Required shareholder return three year	21.00%
Absolute | Out Performance Plan 2017
Out Performance Plan
Required shareholder return three year	21.00%
Relative | Out Performance Plan 2018
Out Performance Plan
Required shareholder return under relative component	3.00%		3.00%
Percentage of shareholder return under which no awards will be earned	0.00%
Relative | Out Performance Plan 2018 | Maximum
Out Performance Plan
Percentage awards will be reduced if total shareholder return is zero or negative	50.00%
SNL US Office REIT Index | Relative | Out Performance Plan 2018
Out Performance Plan
Required shareholder return per year	70.00%
SNL US Retail Index | Relative | Out Performance Plan 2018
Out Performance Plan
Required shareholder return per year	30.00%