Mortgages Payable - Summary of Mortgages Payable (Details) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2019 USD ($) property	Dec. 31, 2018 USD ($) property
Debt
Number of properties | property	60	60
Mortgages Payable
Debt
Number of properties | property	60	60
Weighted Average Stated Interest Rate (as a percent)	5.10%	5.10%
Weighted Average Effective Interest Rate (as a percent)	4.60%	4.60%
Weighted Average Remaining Years Until Maturity	2 years 8 months 12 days	3 years 2 months 12 days
Remaining Principal Balance	$ 295,886	$ 298,377
Unamortized Premium and Deferred Finance Costs Balance, net	3,511	4,192
Net payable amount	$ 299,397	$ 302,569