Concentration of Credit Risk (Details) - Northern New Jersey/New York City ft² in Millions	Sep. 30, 2020 ft² a property
Real Estate Properties [Line Items]
Percentage accounted by properties of its annualized base rent	29.20%
Office building
Real Estate Properties [Line Items]
Number of properties	62
Square feet | ft²	3.6
Land parcels
Real Estate Properties [Line Items]
Number of properties	9
Square feet | a	48.8