Mortgages Payable - Summary of Mortgages Payable (Details) - Mortgages payable $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2020 USD ($) property mortgage	Dec. 31, 2019 USD ($) mortgage property
Debt
Number of Properties | property		68	92
Weighted Average Stated Interest Rate (as a percent)		4.90%	4.90%
Weighted Average Effective Interest Rate (as a percent)		4.60%	4.60%
Weighted Average Remaining Years Until Maturity	3 years 1 month 6 days	2 years 10 months 24 days
Remaining Principal Balance		$ 299,631	$ 408,419
Unamortized Premium and Deferred Finance Costs Balance, net		729	1,700
Net payable amount		$ 300,360	$ 410,119
Number of mortgages | mortgage		18	27
Minimum
Debt
Weighted Average Effective Interest Rate (as a percent)		4.00%	3.80%
Stated interest rate (as a percent)		3.80%	3.80%
Maximum
Debt
Weighted Average Effective Interest Rate (as a percent)		5.50%	7.60%
Stated interest rate (as a percent)		6.90%	6.90%
Variable rate mortgages
Debt
Remaining Principal Balance			$ 7,100