Concentration of Credit Risk (Details) - Northern New Jersey/New York City ft² in Millions	Mar. 31, 2020 a ft² property
Real Estate Properties [Line Items]
Percentage accounted by properties of its annualized base rent	29.70%
Office building
Real Estate Properties [Line Items]
Number of properties	62
Area of real estate property | ft²	3.6
Land parcels
Real Estate Properties [Line Items]
Number of properties	9
Area of real estate property | a	48.7