Mortgages Payable - Narrative (Details) - Mortgages Payable $ in Thousands	9 Months Ended
	Sep. 30, 2019 USD ($) mortgage property	Sep. 30, 2018 USD ($) mortgage	Dec. 31, 2018 USD ($) mortgage property
Debt
Principal amount repaid	$ 19,500	$ 14,600
Number of mortgages assumed | mortgage	0	0
Deferred financing costs	$ 143		$ 183
Number of mortgages | mortgage	25		26
Number of properties with mortgages | property	59		60
Total principal amount	$ 278,882		$ 298,377
Effective yield (as a percent)	4.60%		4.60%
Minimum
Debt
Stated interest rate (as a percent)	3.80%		3.80%
Effective yield (as a percent)	3.80%		1.10%
Maximum
Debt
Stated interest rate (as a percent)	6.90%		6.90%
Effective yield (as a percent)	7.70%		7.70%
Mortgages repaid in full
Debt
Principal amount repaid	$ 15,800	$ 11,000
Number of mortgages repaid | mortgage	1	1
Variable rate mortgages
Debt
Number of mortgages | mortgage	1		2
Number of properties with mortgages | property	1		2
Total principal amount	$ 7,100		$ 23,300
Variable rate mortgages after interest rate arrangements
Debt
Total principal amount			$ 16,000