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Revenue derived from construction, architectural services and supervision of capital projects provided under contracts or arrangements with clients.

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Represents the number of limited partnerships and limited liability companies in which the entity has made investments which are accounted for using the equity method of consolidation.

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Number of employees, excluding President, having ownership interest in the investment properties.

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Revenue from a related party for maintenace services.

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Amounts charged by related party for services provided during the financial reporting period, excluding management fee. Services may include legal, accounting, administrative, repairs and maintenance, construction, rental and architectural services and supervision of capital projects.

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Revenue derived from rental commissions.

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

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Amount of cost for defined contribution plan.

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Amount of the cost of borrowed funds accounted for as interest expense.

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Amount of commissions expense incurred because the lessor of real estate obtained a lessee for a rental property through a real estate agent.

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The amount of cash paid for brokerage fees during the current period. This element is intended to represent the brokerage fees paid by and between financial industry participants.

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The percentage charged for managing real estate properties.

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The amount of revenue derived from managing real estate properties.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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RELATED PARTY TRANSACTIONS (Details)	12 Months Ended
RELATED PARTY TRANSACTIONS (Details)	Dec. 31, 2018 USD ($) item	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 29, 2017 USD ($)	Jul. 16, 2017 USD ($)	Jul. 06, 2017 USD ($)
RELATED PARTY TRANSACTIONS
Management fee	$ 2,326,225	$ 2,159,458	$ 2,029,171
Repairs and maintenance	9,187,714	8,378,639	8,258,263
Administrative expense	$ 2,204,923	2,008,107	2,102,812
Number of advisory committee meetings \| item	4
Expenses incurred for advisory committee meeting	$ 21,000
Number of audit committee meetings held \| item	4
Expenses incurred for audit committee meeting	$ 14,000
Interest expense	$ 12,389,680	11,114,146	10,200,393
Majority of Partnership Properties, Excluding Linewt
RELATED PARTY TRANSACTIONS
Management fee as percentage of gross receipts rental revenue	4.00%
Hamilton Linewt LLC Commercial-1031 Exchange Newton, Massachusetts
RELATED PARTY TRANSACTIONS
Management fee as percentage of gross receipts rental revenue	3.00%
Woodland Park Apartments LLC Newton Massachusetts
RELATED PARTY TRANSACTIONS
Loan amount						$ 22,250,000	$ 16,000,000	$ 16,000,000
Interest rate (as a percent)						3.79%	4.75%
Interest expense	$ 182,000
Investment Properties
RELATED PARTY TRANSACTIONS
Number of limited partnerships and limited liability companies in which the entity has invested \| item	8
Investment Properties \| Minimum
RELATED PARTY TRANSACTIONS
Ownership interest (as a percent)	40.00%
Investment Properties \| Maximum
RELATED PARTY TRANSACTIONS
Ownership interest (as a percent)	50.00%
Hamilton Company/Management Company
RELATED PARTY TRANSACTIONS
Employer contributions in 401K plan	$ 0	0	0
Number of accounting staff of related party providing bookkeeping and accounting functions \| item	14
Hamilton Company/Management Company, Related Party
RELATED PARTY TRANSACTIONS
Management fee	$ 2,326,000	2,159,000	2,029,000
Related Party Transaction, Services, Excluding Management Fee	1,380,000	882,000	1,069,000
Repairs and maintenance	433,000
Administrative expense	349,000
Commercial brokerage fees	21,000
Rental commissions	13,000
Construction, architectural services and supervision of capital projects	564,000
Amount received for rental commissions	299,000
Reimbursement to related party for payroll transfers	3,347,000	3,463,000	3,076,000
Fees for accounting and bookkeeping services	125,000	125,000	125,000
Investment Properties \| Hamilton Company/Management Company
RELATED PARTY TRANSACTIONS
Property Management Fee Revenue And Other Service Revenue	1,263,000
Amount received for management fees	652,000
Amount received for construction, architectural services and supervision of capital projects	210,000
Amount received for maintenance services	47,000
Amount received for administrative services	$ 54,000
Number of employees having ownership interest in the investment properties \| item	5
Investment Properties, Excluding Dexter Park \| Hamilton Company/Management Company
RELATED PARTY TRANSACTIONS
Property management fee received (as a percent)	4.00%
Dexter Park \| Hamilton Company/Management Company
RELATED PARTY TRANSACTIONS
Property management fee received (as a percent)	2.00%
President of Management Company
RELATED PARTY TRANSACTIONS
Quarterly fee for asset management consulting services			18,750	$ 18,750	$ 18,750
Annual fee for asset management consulting services	$ 37,500	$ 75,000	$ 75,000
Harold Brown \| Investment Properties \| Minimum
RELATED PARTY TRANSACTIONS
Ownership interest of related party (as a percent)	47.60%
Harold Brown \| Investment Properties \| Maximum
RELATED PARTY TRANSACTIONS
Ownership interest of related party (as a percent)	59.00%
Residential and mixed-use properties \| Partially owned properties \| Minimum
RELATED PARTY TRANSACTIONS
Ownership interest (as a percent)	40.00%
Residential and mixed-use properties \| Partially owned properties \| Investment Properties \| Minimum
RELATED PARTY TRANSACTIONS
Ownership interest (as a percent)	40.00%
Residential and mixed-use properties \| Partially owned properties \| Investment Properties \| Maximum
RELATED PARTY TRANSACTIONS
Ownership interest (as a percent)	50.00%