Mortgages payable and credit line (Narrative) (Details) - USD ($)								1 Months Ended								2 Months Ended	3 Months Ended	12 Months Ended
	Jan. 10, 2022	Feb. 06, 2021	Aug. 26, 2019	Apr. 03, 2019	Feb. 07, 2018	Dec. 07, 2017	Jan. 14, 2013	Dec. 30, 2021	Feb. 28, 2021	Sep. 30, 2020	Jun. 30, 2019	May 31, 2018	Apr. 28, 2017	Sep. 29, 2016	Apr. 22, 2016	Nov. 05, 2020	Jun. 30, 2020	Oct. 31, 2021	Oct. 31, 2020	Jul. 31, 2018	Dec. 26, 2012
Debt Instrument [Line Items]
Legal fees																		$ 2,282,000	$ 957,000
Line of Credit [Member]
Debt Instrument [Line Items]
Basis points, interest rate																		3.75%
Maturity date of loan																		Oct. 31, 2023
Line of Credit, available																		$ 13,000,000
Station Place on Monmouth, LLC [Member]
Debt Instrument [Line Items]
Basis points, interest rate						1.80%
Fixed interest rate current loan						4.35%
Loan amount						$ 12,350,000
Maturity date of loan						Dec. 15, 2027
Term of the loan						2 years
WestFREIT Corp [Member]
Debt Instrument [Line Items]
Refinanced loan amount													$ 22,000,000
Basis points, interest rate													2.75%
Debt Instrument, Periodic Payment											$ 45,250	$ 43,250
Loan amount													$ 23,500,000
Maturity date of loan													Apr. 28, 2019
Net proceeds from refinancing of debt													$ 1,100,000
Description of loan amendment terms													This refinancing resulted in: (i) a reduction in the annual interest rate from a fixed rate of 5.55% to a variable rate
Wells Fargo Bank [Member]
Debt Instrument [Line Items]
Amount repaid					$ 115,300,000
Aareal Capital Corporation [Member]
Debt Instrument [Line Items]
Variable interest rate																		2.93%
Interest rate cap		3.00%
Loan amount		$ 118,500,000																$ 116,500,000
Amount repaid		$ 500,000
Maturity date of loan		Feb. 06, 2022
Mortgages [Member]
Debt Instrument [Line Items]
Fixed rate mortgage loans																		138,568,000	141,945,000
Debt Instrument, Periodic Payment																$ 319,000	$ 390,000
Loan amount																		22,600,000
Deferred Interest																$ 138,000	$ 222,000
Mortgages [Member] | Rockaway, NJ Mortgage [Member]
Debt Instrument [Line Items]
Refinanced loan amount								$ 7,500,000
Fixed rate mortgage loans																		$ 14,453,000	15,050,000
Fixed interest rate current loan																		5.37%
Debt Instrument, Periodic Payment																		$ 115,850
Debt Instrument, collateral amount																		14,532,000
Mortgages [Member] | Westwood, NJ#1 [Member]
Debt Instrument [Line Items]
Refinanced loan amount							$ 8,000,000.0
Mortgages [Member] | Westwood, NJ #2 [Member]
Debt Instrument [Line Items]
Fixed rate mortgage loans																		$ 18,001,000	18,695,000
Fixed interest rate current loan																		4.75%
Debt Instrument, Periodic Payment																		$ 129,702
Debt Instrument, collateral amount																		7,051,000
Loan amount																		22,750,000
Mortgages [Member] | Wayne, NJ Mortgage [Member] | Berdan Court, LLC [Member]
Debt Instrument [Line Items]
Refinanced loan amount			$ 17,000,000
Fixed interest rate on old loan			6.09%
Fixed rate mortgage loans																		28,815,000	28,815,000
Fixed interest rate current loan			3.54%
Debt Instrument, Periodic Payment			$ 85,004
Debt Instrument, collateral amount																		$ 1,490,000
Loan amount			$ 28,815,000
Maturity date of loan			Sep. 01, 2029
Term of the loan			5 years
Net proceeds from refinancing of debt			$ 11,600,000
Future periodic payment including principal			$ 130,036
Mortgages [Member] | River Edge, NJ Refinanced Mortgage [Member]
Debt Instrument [Line Items]
Fixed interest rate current loan																		4.54%
Debt Instrument, Periodic Payment																		$ 57,456
Debt Instrument, collateral amount																		679,000
Loan amount																		11,200,000
Mortgages [Member] | Red Bank, NJ Refinanced Mortgage [Member]
Debt Instrument [Line Items]
Debt Instrument, collateral amount																		18,514,000
Mortgages [Member] | Wayne, PSC LLC [Member]
Debt Instrument [Line Items]
Refinanced loan amount														$ 24,200,000				$ 25,800,000
Basis points, interest rate																		2.20%
Fixed interest rate on old loan																		6.04%
Fixed rate mortgage loans																		$ 22,588,000	23,336,000
Fixed interest rate current loan																		3.625%
Membership interest percentage																		40.00%
Debt Instrument, collateral amount																		$ 23,408,000
Debt Instrument, collateral amount classified as construction in progress																		400,000
Loan amount																		$ 25,800,000
Description of variable interest rate																		a reduction in interest rate from 6.04% to 3.625%
Maturity date of loan																		Oct. 01, 2026
Net proceeds from refinancing of debt																		$ 1,000,000
Mortgages [Member] | S And A Commercial Associates Limited Partnership [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Net proceeds from refinancing of debt	$ 18,200,000
Mortgages [Member] | Damascus, MD [Member]
Debt Instrument [Line Items]
Fixed interest rate tranche one																		3.81%
Fixed interest rate tranche two																		3.53%
Mortgages [Member] | Damascus, MD [Member]
Debt Instrument [Line Items]
Fixed rate mortgage loans																		$ 18,274,000	18,824,000
Maturity date of loan																		Jan. 03, 2023
Net proceeds from refinancing of debt																					$ 20,000,000
Monthly principal payment amount															$ 2,320,000
Line of Credit, available															470,000
Escrow released															$ 1,850,000					$ 1,850,000
Mortgages [Member] | Damascus, MD [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Debt Instrument, Periodic Payment	$ 18,200,000
Mortgages [Member] | Middletown, NY Mortgage [Member]
Debt Instrument [Line Items]
Fixed rate mortgage loans																		$ 14,921,000	15,255,000
Mortgages [Member] | Frederick, MD [Member]
Debt Instrument [Line Items]
Debt Instrument, collateral amount																		11,626,000
Mortgages [Member] | Westwood Hills Property [Member]
Debt Instrument [Line Items]
Refinanced loan amount										$ 25,000,000
Basis points, interest rate										4.00%
Fixed rate mortgage loans										$ 19,200,000
Loan amount																		8,207,000
Maturity date of loan										Oct. 01, 2022
Legal fees										$ 250,000
Mortgages [Member] | Westwood Hills Property [Member] | Maximum [Member]
Debt Instrument [Line Items]
Fixed interest rate on old loan										4.62%
Mortgages [Member] | Westwood Hills Property [Member] | Minimum [Member]
Debt Instrument [Line Items]
Fixed interest rate on old loan										4.15%
Mortgages [Member] | COVID 19 [Member]
Debt Instrument [Line Items]
Deferred Interest																			162,100
Deferred payments																			$ 303,800
Remaining deferred Amount																		$ 141,700
Provident Bank [Member] | Middletown, NY Mortgage [Member]
Debt Instrument [Line Items]
Basis points, interest rate																		1.25%
Fixed interest rate current loan																		3.75%
Debt Instrument, collateral amount																		$ 17,935,000
Loan amount																		$ 16,200,000
Maturity date of loan																		Dec. 15, 2024
Monthly principal payment amount																		$ 27,807
WestFREIT Corp [Member]
Debt Instrument [Line Items]
Basis points, interest rate				2.40%					2.55%
Fixed interest rate current loan																		2.68%
Debt Instrument, Periodic Payment				$ 47,250					$ 49,250
Loan amount				$ 22,500,000														$ 21,100,000
Maturity date of loan				May 01, 2020					Jan. 31, 2022
Rotunda [Member]
Debt Instrument [Line Items]
Basis points, interest rate																		2.85%
Debt Instrument, collateral amount																		$ 136,623,000
Loan amount																		$ 118,500,000
Maturity date of loan																		Feb. 06, 2021
Rotunda [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Loan amount								$ 116,500,000
Grande Rotunda LLC Construction Loan [Member]
Debt Instrument [Line Items]
Interest rate cap																		3.00%
Loan amount																		$ 121,900,000
Line of Credit, available																		$ 3,380,000