COVID-19 Pandemic - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Jun. 30, 2019
Unusual or Infrequent Item, or Both [Line Items]
Reduction of rental revenues		$ 1,022	$ 0
COVID-19
Unusual or Infrequent Item, or Both [Line Items]
Rent collected, percent	89.00%
Rent collected & deferred, percent	92.00%
Reduction of rental revenues	$ 1,022	1,022
Write-off of rent receivable	$ 4,247	$ 4,247
Office | 731 Lexington Avenue | COVID-19
Unusual or Infrequent Item, or Both [Line Items]
Rent collected, percent	100.00%
Retail | COVID-19
Unusual or Infrequent Item, or Both [Line Items]
Rent collected, percent	76.00%
Rent collected & deferred, percent	83.00%
Residential | Alexander Apartment Tower | COVID-19
Unusual or Infrequent Item, or Both [Line Items]
Rent collected, percent	96.00%