Real Estate (Narrative) (Details) - ft²	Feb. 25, 2021	Feb. 01, 2021
One Five Nine East 53rd Street
Real Estate Properties [Line Items]
Net Rentable Area (in sf)		220,000
Construction in Progress | 180 CityPoint
Real Estate Properties [Line Items]
Net Rentable Area (in sf)	329,000
Construction in Progress | 880 Winter Street [Member]
Real Estate Properties [Line Items]
Net Rentable Area (in sf)	224,000
Construction in Progress | The Prudential Center Observatory
Real Estate Properties [Line Items]
Net Rentable Area (in sf)	59,000