Interest rate cap and swap contracts (Details) - USD ($)			1 Months Ended	3 Months Ended			6 Months Ended
	Feb. 07, 2018	Dec. 07, 2017	Sep. 29, 2016	Apr. 30, 2020	Feb. 28, 2020	Apr. 30, 2019	Apr. 30, 2020	Apr. 30, 2019	Oct. 31, 2019	Apr. 22, 2016	Dec. 26, 2012
Derivative [Line Items]
Mortgages payable				$ 302,912,000			$ 302,912,000		$ 352,790,000
Interest rate swap contract liability				5,498,000			5,498,000		2,126,000
Unrealized loss on derivatives						$ 5,000		$ 159,000
Net unrealized gain (loss) on interest rate swap contracts				(2,982,000)		(821,000)	(3,372,000)	(3,185,000)
Damascus Centre Swap [Member]
Derivative [Line Items]
Interest rate swap contract liability				730,000			730,000
Wayne PSC swap [Member]
Derivative [Line Items]
Interest rate swap contract liability				1,394,000			1,394,000
Regency Swap [Member]
Derivative [Line Items]
Interest rate swap contract liability				1,523,000			1,523,000
Station Place [Member]
Derivative [Line Items]
Interest rate swap contract liability				1,851,000			1,851,000
Grande Rotunda LLC [Member]
Derivative [Line Items]
Interest rate swap contract liability				0			0
Station Place [Member]
Derivative [Line Items]
Loan amount		$ 12,350,000		12,300,000			12,300,000
Notional amount of interest rate swap				12,300,000			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						$ 5,000		$ 159,000
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 Loan [Member]
Derivative [Line Items]
Loan amount				118,500,000			118,500,000
Notional amount of interest rate cap				$ 121,900,000	$ 121,900,000		$ 121,900,000
Interest rate cap				3.00%	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	$ 23,400,000			$ 23,400,000
Notional amount of interest rate swap				23,400,000			23,400,000
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				19,100,000			19,100,000
Mortgages payable										$ 2,320,000
Notional amount of interest rate swap				$ 19,100,000			$ 19,100,000
People's United Bank [Member] | Tranche One [Member]
Derivative [Line Items]
Loan amount											$ 20,000,000
Fixed interest rate				3.81%			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%			3.53%
Regency Loan [Member]
Derivative [Line Items]
Refinanced loan amount							$ 16,200,000
Loan amount				$ 15,400,000			15,400,000
Notional amount of interest rate swap				$ 15,400,000			$ 15,400,000
Fixed interest rate				3.75%			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