Concentration of Credit Risk (Details) ft² in Millions	Dec. 31, 2019 a ft² property
Real Estate Properties [Line Items]
Number of properties	220
Area of real estate property | a	77.6
Northern New Jersey/New York City [Member]
Real Estate Properties [Line Items]
Percentage accounted by properties of its annualized base rent	30.90%
Northern New Jersey/New York City [Member] | Office building [Member]
Real Estate Properties [Line Items]
Number of properties	62
Area of real estate property | ft²	3.6
Northern New Jersey/New York City [Member] | Land parcels [Member]
Real Estate Properties [Line Items]
Number of properties	9
Area of real estate property | a	48.7