Mortgages Payable - Summary of Mortgages Payable (Details) - Mortgages payable $ in Thousands	Jun. 30, 2021	Dec. 31, 2020 USD ($) property mortgage	Sep. 30, 2021 USD ($) mortgage property
Debt
Number of Properties | property		68	61
Weighted Average Stated Interest Rate (as a percent)		4.90%	4.40%
Weighted Average Effective Interest Rate (as a percent)		4.60%	4.30%
Weighted Average Remaining Years Until Maturity	2 years 2 months 12 days	2 years 10 months 24 days
Remaining Principal Balance		$ 299,631	$ 285,549
Unamortized Premium and Deferred Finance Costs Balance, net		729	68
Net payable amount		$ 300,360	$ 285,617
Number of mortgages | mortgage		18	13
Minimum
Debt
Weighted Average Effective Interest Rate (as a percent)		4.00%	2.80%
Stated interest rate (as a percent)		3.80%	3.00%
Maximum
Debt
Weighted Average Effective Interest Rate (as a percent)		5.50%	4.90%
Stated interest rate (as a percent)		6.90%	6.90%