Interest rate cap and swap contracts (Details) - USD ($)			1 Months Ended	3 Months Ended
	Feb. 07, 2018	Dec. 07, 2017	Sep. 29, 2016	Feb. 28, 2020	Jan. 31, 2020	Jan. 31, 2019	Oct. 31, 2019	Apr. 22, 2016	Dec. 26, 2012
Derivative [Line Items]
Mortgages payable					$ 351,752,000		$ 352,790,000
Interest rate swap contract liability					2,516,000		2,126,000
Unrealized loss on derivatives						$ 154,000
Net unrealized gain (loss) on interest rate swap contracts					(390,000)	$ (2,364,000)
Damascus Centre Swap [Member]
Derivative [Line Items]
Interest rate swap contract liability					239,000
Wayne PSC swap [Member]
Derivative [Line Items]
Interest rate swap contract liability					238,000
Regency Swap [Member]
Derivative [Line Items]
Interest rate swap contract liability					917,000
Station Place [Member]
Derivative [Line Items]
Interest rate swap contract liability					1,122,000
Grande Rotunda LLC [Member]
Derivative [Line Items]
Interest rate swap contract liability					0
Station Place [Member]
Derivative [Line Items]
Loan amount		$ 12,350,000			12,300,000
Notional amount of interest rate swap					12,300,000
Fixed interest rate		4.35%
Interest rate swap contract liability							1,034,000
Basis points, interest rate		1.80%
Maturity date of interest rate cap		Dec. 15, 2027
Grande Rotunda LLC [Member]
Derivative [Line Items]
Interest rate cap contract liability							0
Unrealized loss on derivatives					154,000
Wells Fargo Bank [Member]
Derivative [Line Items]
Loan amount	$ 115,300,000
Aareal Capital Corporation [Member]
Derivative [Line Items]
Loan amount	118,500,000
Available to draw	$ 3,380,000
Basis points, interest rate	2.85%
Maturity date of loan	Feb. 06, 2021
Grande Rotunda LLC [Member]
Derivative [Line Items]
Loan amount					$ 118,500,000
Interest rate cap				3.00%	3.00%
Basis points, interest rate					2.85%
Maturity date of interest rate cap				Mar. 05, 2021
Grande Rotunda LLC Loan [Member]
Derivative [Line Items]
Loan amount					$ 118,500,000
Notional amount of interest rate cap				$ 121,900,000	$ 121,900,000
Interest rate cap				3.00%	3.00%
Maturity date of interest rate cap				Mar. 05, 2021	Mar. 05, 2020
Wayne PSC, LLC Loan [Member]
Derivative [Line Items]
Refinanced loan amount			$ 24,200,000
Loan amount			$ 25,800,000		$ 23,600,000
Notional amount of interest rate swap					23,600,000
Fixed interest rate			3.625%
Basis points, interest rate			2.20%
Maturity date of interest rate cap			Oct. 01, 2026
People's United Bank [Member]
Derivative [Line Items]
Loan amount					19,200,000
Mortgages payable								$ 2,320,000
Notional amount of interest rate swap					$ 19,300,000
People's United Bank [Member] | Tranche One [Member]
Derivative [Line Items]
Loan amount									$ 20,000,000
Fixed interest rate					3.81%
Basis points, interest rate					2.10%
Maturity date of loan					Jan. 03, 2023
People's United Bank [Member] | Tranche Two [Member]
Derivative [Line Items]
Loan amount								$ 2,320,000
Fixed interest rate					3.53%
Regency Loan [Member]
Derivative [Line Items]
Refinanced loan amount					$ 16,200,000
Loan amount					15,500,000
Notional amount of interest rate swap					$ 15,500,000
Fixed interest rate					3.75%
Basis points, interest rate					1.25%
Maturity date of loan					Dec. 15, 2024
Damascus Centre [Member]
Derivative [Line Items]
Interest rate swap contract liability							179,000
Wayne PSC swap [Member]
Derivative [Line Items]
Interest rate swap contract liability							53,000
Regency Swap [Member]
Derivative [Line Items]
Interest rate swap contract liability							$ 860,000