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Represents the aggregate purchase price of real estate properties acquired by the entity allocated to tenant relationships.

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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Face (par) amount of debt instrument at time of issuance.

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Contractual interest rate for funds borrowed, under the debt agreement.

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Period between issuance and maturity of long-term debt, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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The number of units in a real estate property owned as of the balance sheet date.

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Amount of cash outflow for cost from early extinguishment and prepayment of debt. Includes, but is not limited to, third-party cost, premium paid, and other fee paid to lender directly for debt extinguishment or debt prepayment. Excludes accrued interest.

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MORTGAGE NOTES PAYABLE (Mortgage by property) (Details)	Mar. 31, 2020 USD ($)	Dec. 20, 2019 USD ($) item	May 31, 2019 USD ($)	Mar. 29, 2018 USD ($) item	Mar. 12, 2018 USD ($)	Dec. 31, 2020 USD ($) item	Dec. 31, 2019 USD ($) item	Dec. 31, 2018 item	Sep. 30, 2015 USD ($)
MORTGAGE NOTES PAYABLE
Line of credit							$ 17,000,000
Residences at Captain Parkers LLC Residential Apartments Lexington, Massachusetts
MORTGAGE NOTES PAYABLE
Loan amount			$ 20,750,000
Interest rate (as a percent)			4.05%
Loan balance			$ 20,071,000
Mortgage prepayment penalties			$ 202,000
57 Mill Street
MORTGAGE NOTES PAYABLE
Number of units \| item		181
Loan amount		$ 31,000,000
Purchase price of real estate properties		59,550,000
Cash from reserves		10,550,000
Line of credit		18,000,000
Closing Costs		237,000
Purchase price allocated to the value of the in-place leases		1,282,000
Purchase price allocated to the value of the tenant relationships		$ 136,000
Amortization period of value of the in-place leases		12 months
Amortization period of value of the tenant relationships		36 months
Hamilton Essex 81
MORTGAGE NOTES PAYABLE
Number of units \| item						49	49	49
Loan amount									$ 10,000,000
Loan balance						$ 10,000,000
Hamilton Highlands LLC Residential Needham Massachusetts [Member]
MORTGAGE NOTES PAYABLE
Number of units \| item				79
Loan amount				$ 21,500,000
Purchase price of real estate properties				34,500,000
Cash payment				13,000,000
Cash from reserves				5,000,000
Line of credit				8,000,000
Closing costs associated with financing				141,000
Purchase price allocated to the value of the in-place leases				502,000
Purchase price allocated to the value of the tenant relationships				$ 40,000
Amortization period of value of the in-place leases				12 months
Amortization period of value of the tenant relationships				24 months
659 Worcester Road
MORTGAGE NOTES PAYABLE
Loan amount					$ 6,083,683
Closing Costs					$ 69,000
Interest rate (as a percent)					4.87%
Amortization period of debt					30 years
Monthly payment amount					$ 32,427
Debt Instrument, Amortization Term					30 years
Brookside Associates LLC Residential Apartments Woburn, Massachusetts
MORTGAGE NOTES PAYABLE
Loan amount	$ 6,175,000
Repayment of loan	2,390,000
Closing Costs	$ 136,000
Interest rate (as a percent)	3.53%
Initial Advance \| 57 Mill Street
MORTGAGE NOTES PAYABLE
Loan amount		$ 31,000,000
Interest rate (as a percent)		3.586%
Subsequent Advance \| 57 Mill Street
MORTGAGE NOTES PAYABLE
Loan amount		$ 4,000,000
Interest rate (as a percent)		3.50%
Maximum \| 57 Mill Street
MORTGAGE NOTES PAYABLE
Loan amount		$ 35,000,000
Mortgages payable
MORTGAGE NOTES PAYABLE
Loan balance						$ 284,790,000
Mortgages payable \| Minimum
MORTGAGE NOTES PAYABLE
Interest rate (as a percent)						3.53%
Mortgages payable \| Maximum
MORTGAGE NOTES PAYABLE
Interest rate (as a percent)						5.66%