Concentration of Credit Risk (Details) - Northern New Jersey/New York City ft² in Millions	Mar. 31, 2021 a ft² property
Real Estate Properties
Percentage accounted by properties of its annualized base rent	28.30%
Office building
Real Estate Properties
Number of properties	63
Area of real estate property | ft²	3.6
Land
Real Estate Properties
Number of properties	9
Area of real estate property | a	48.6