Mortgages Payable - Summary of Mortgages Payable (Details) - Mortgages Payable $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019 USD ($) property	Dec. 31, 2018 USD ($) property
Debt
Number of properties | property	59	60
Weighted Average Stated Interest Rate (as a percent)	5.20%	5.10%
Weighted Average Effective Interest Rate (as a percent)	4.60%	4.60%
Weighted Average Remaining Years Until Maturity	2 years 7 months 6 days	3 years 2 months 12 days
Remaining Principal Balance	$ 278,882	$ 298,377
Unamortized Premium and Deferred Finance Costs Balance, net	3,171	4,192
Net payable amount	$ 282,053	$ 302,569