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Debt - Mortgages Payable (Details) - USD ($)	6 Months Ended
Debt - Mortgages Payable (Details) - USD ($)	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Debt Instrument [Line Items]
Total	$ 783,900,000,000
Long-term Debt, Total	783,878,000
Repayments Of Secured Debt	3,238,000	$ 1,353,000
Mortgages [Member]
Debt Instrument [Line Items]
Total	33,878,000		$ 37,115,000
Unamortized debt issuance costs	(365,000)		(417,000)
Long-term Debt, Total	33,513,000		36,698,000
Notes Payable Due February 2020 6.24 Percent [Member] \| Mortgages [Member]
Debt Instrument [Line Items]
Total			2,775,000
Debt Instrument, Periodic Payment, Principal	$ 23,004
Debt Instrument, Interest Rate, Stated Percentage	6.24%
Notes Payable Due January 2023 3.60 Percent [Member] \| Mortgages [Member]
Debt Instrument [Line Items]
Total	$ 23,640,000		23,640,000
Debt Instrument, Interest Rate, Stated Percentage	3.60%
Notes Payable Due September 2023 5.01 Percent [Member] \| Mortgages [Member]
Debt Instrument [Line Items]
Total	$ 4,686,000		4,779,000
Debt Instrument, Periodic Payment, Principal	35,673
Debt Instrument, Periodic Payment Terms, Balloon Payment to be Paid	$ 4,034,627
Debt Instrument, Interest Rate, Stated Percentage	5.01%
Notes Payable Due July 2026 6.27 Percent [Member] \| Mortgages [Member]
Debt Instrument [Line Items]
Total	$ 5,552,000		$ 5,921,000
Debt Instrument, Periodic Payment, Principal	$ 91,675
Debt Instrument, Interest Rate, Stated Percentage	6.27%