COVID-19 Pandemic (Narrative) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Oct. 31, 2020	Apr. 30, 2020 employee	Apr. 01, 2020 USD ($)
Unusual or Infrequent Item, or Both [Line Items]
Income tax benefit	$ (23,781,000)	$ (23,885,000)	$ (38,431,000)	$ (80,542,000)
Hotel Pennsylvania
Unusual or Infrequent Item, or Both [Line Items]
Restructuring reserve, accrual	9,246,000		9,246,000
Income tax benefit	$ 3,145,000		3,145,000
COVID-19
Unusual or Infrequent Item, or Both [Line Items]
Number of employees furloughed | employee						1,803
Rent collected, percent	93.00%
Rent collected (including deferrals), percent	95.00%
Write off of tenant receivables deemed uncollectible	$ 12,364,000		21,186,000
COVID-19 | Office Space
Unusual or Infrequent Item, or Both [Line Items]
Rent collected, percent	95.00%
Rent collected (including deferrals), percent	97.00%
COVID-19 | Retail
Unusual or Infrequent Item, or Both [Line Items]
Rent collected, percent	82.00%
Rent collected (including deferrals), percent	85.00%
COVID-19 | 330 West 34th Street
Unusual or Infrequent Item, or Both [Line Items]
Write off of receivables arising from the straight-lining of rents	$ 13,873,000		$ 50,170,000
COVID-19 | Non-Management Member Board of Trustees
Unusual or Infrequent Item, or Both [Line Items]
Annual cash retainer forgone							$ 75,000
COVID-19 | Hotel Pennsylvania
Unusual or Infrequent Item, or Both [Line Items]
Number of employees furloughed | employee						414
COVID-19 | Building Maintenance Service LLC
Unusual or Infrequent Item, or Both [Line Items]
Number of employees furloughed | employee						1,293
COVID-19 | Vornado Realty Trust
Unusual or Infrequent Item, or Both [Line Items]
Number of employees furloughed | employee						96
COVID-19 | Vornado Realty Trust | Subsequent Event
Unusual or Infrequent Item, or Both [Line Items]
Percentage of employees returned from furlough					40.00%