RENTAL PROPERTIES - Real Estate Detail (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2016
Real estate and accumulated depreciation
Encumbrances (First Mortgages)	$ 373,190,322
Initial Cost to Partnerships
Land	75,124,253
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	42,477,504
Gross Amount at Which Carried at Close of Period
Land	75,280,781
Building Improvements	325,307,458
Totals	400,588,242	$ 398,629,793	$ 398,554,000	$ 337,902,411
Accumulated Depreciation	149,233,040	$ 134,019,906	$ 120,190,012	$ 107,391,148
Buildings and improvements
Initial Cost to Partnerships
Building Improvements	$ 282,829,954
Buildings and improvements | Minimum
Gross Amount at Which Carried at Close of Period
Estimated useful lives	10 years
Buildings and improvements | Maximum
Gross Amount at Which Carried at Close of Period
Estimated useful lives	40 years
Other Categories of Assets | Minimum
Gross Amount at Which Carried at Close of Period
Estimated useful lives	5 years
Other Categories of Assets | Maximum
Gross Amount at Which Carried at Close of Period
Estimated useful lives	15 years
Boylston Downtown L.P. Residential Apartments Boston, Massachusetts
Real estate and accumulated depreciation
Encumbrances (First Mortgages)	$ 35,877,479
Initial Cost to Partnerships
Land	2,112,000
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	10,320,968
Gross Amount at Which Carried at Close of Period
Land	2,268,528
Building Improvements	18,914,077
Totals	21,182,605
Accumulated Depreciation	15,426,451
Boylston Downtown L.P. Residential Apartments Boston, Massachusetts | Buildings and improvements
Initial Cost to Partnerships
Building Improvements	8,593,109
Brookside Associates LLC Residential Apartments Woburn, Massachusetts
Real estate and accumulated depreciation
Encumbrances (First Mortgages)	6,175,000
Initial Cost to Partnerships
Land	684,000
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	411,502
Gross Amount at Which Carried at Close of Period
Land	684,000
Building Improvements	3,527,502
Totals	4,211,502
Accumulated Depreciation	2,688,358
Brookside Associates LLC Residential Apartments Woburn, Massachusetts | Buildings and improvements
Initial Cost to Partnerships
Building Improvements	3,116,000
Clovelly Apartments L.P. Residential Apartments Nashua, New Hampshire
Real estate and accumulated depreciation
Encumbrances (First Mortgages)	11,214,000
Initial Cost to Partnerships
Land	177,610
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	1,590,269
Gross Amount at Which Carried at Close of Period
Land	177,610
Building Improvements	3,068,628
Totals	3,246,238
Accumulated Depreciation	2,444,383
Clovelly Apartments L.P. Residential Apartments Nashua, New Hampshire | Buildings and improvements
Initial Cost to Partnerships
Building Improvements	1,478,359
Commonwealth 1137 L.P. Residential Apartments Boston, Massachusetts
Real estate and accumulated depreciation
Encumbrances (First Mortgages)	5,440,000
Initial Cost to Partnerships
Land	342,000
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	973,511
Gross Amount at Which Carried at Close of Period
Land	342,000
Building Improvements	2,341,180
Totals	2,683,180
Accumulated Depreciation	1,991,634
Commonwealth 1137 L.P. Residential Apartments Boston, Massachusetts | Buildings and improvements
Initial Cost to Partnerships
Building Improvements	1,367,669
Commonwealth 1144 L.P. Residential Apartments Boston, Massachusetts
Real estate and accumulated depreciation
Encumbrances (First Mortgages)	32,325,000
Initial Cost to Partnerships
Land	1,410,000
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	4,296,087
Gross Amount at Which Carried at Close of Period
Land	1,410,000
Building Improvements	9,960,903
Totals	11,370,903
Accumulated Depreciation	7,566,432
Commonwealth 1144 L.P. Residential Apartments Boston, Massachusetts | Buildings and improvements
Initial Cost to Partnerships
Building Improvements	5,664,816
Executive Apartments L.P. Residential Apartments Framingham, Massachusetts
Real estate and accumulated depreciation
Encumbrances (First Mortgages)	8,190,000
Initial Cost to Partnerships
Land	91,400
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	1,451,297
Gross Amount at Which Carried at Close of Period
Land	91,400
Building Improvements	2,191,657
Totals	2,283,057
Accumulated Depreciation	1,542,613
Executive Apartments L.P. Residential Apartments Framingham, Massachusetts | Buildings and improvements
Initial Cost to Partnerships
Building Improvements	740,360
Hamilton Battle Green LLC Residential Apartments Lexington, Massachusetts
Real estate and accumulated depreciation
Encumbrances (First Mortgages)	4,020,965
Initial Cost to Partnerships
Land	1,341,737
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	130,841
Gross Amount at Which Carried at Close of Period
Land	1,341,737
Building Improvements	8,588,338
Totals	9,930,075
Accumulated Depreciation	3,656,897
Hamilton Battle Green LLC Residential Apartments Lexington, Massachusetts | Buildings and improvements
Initial Cost to Partnerships
Building Improvements	8,457,497
Hamilton Cypress LLC Commercial-1031Exchange Brookline, Massachusetts
Initial Cost to Partnerships
Land	2,362,596
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	19,392
Gross Amount at Which Carried at Close of Period
Land	2,362,596
Building Improvements	4,633,377
Totals	6,995,973
Accumulated Depreciation	1,715,282
Hamilton Cypress LLC Commercial-1031Exchange Brookline, Massachusetts | Buildings and improvements
Initial Cost to Partnerships
Building Improvements	4,613,985
Hamilton Green Apartments Residential Apartments Andover, Massachusetts
Real estate and accumulated depreciation
Encumbrances (First Mortgages)	33,783,041
Initial Cost to Partnerships
Land	16,054,336
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	(8,374,341)
Gross Amount at Which Carried at Close of Period
Land	16,054,336
Building Improvements	36,420,097
Totals	52,474,433
Accumulated Depreciation	13,687,188
Hamilton Green Apartments Residential Apartments Andover, Massachusetts | Buildings and improvements
Initial Cost to Partnerships
Building Improvements	44,794,438
Hamilton Highlands LLC Residential Needham Massachusetts [Member]
Real estate and accumulated depreciation
Encumbrances (First Mortgages)	20,086,380
Initial Cost to Partnerships
Land	6,815,522
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	704,759
Gross Amount at Which Carried at Close of Period
Land	6,815,522
Building Improvements	27,966,846
Totals	34,782,368
Accumulated Depreciation	6,453,152
Hamilton Highlands LLC Residential Needham Massachusetts [Member] | Buildings and improvements
Initial Cost to Partnerships
Building Improvements	27,262,087
Hamilton Linewt LLC Commercial-1031 Exchange Newton, Massachusetts
Initial Cost to Partnerships
Land	884,042
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	134,614
Gross Amount at Which Carried at Close of Period
Land	884,042
Building Improvements	2,786,741
Totals	3,670,783
Accumulated Depreciation	987,705
Hamilton Linewt LLC Commercial-1031 Exchange Newton, Massachusetts | Buildings and improvements
Initial Cost to Partnerships
Building Improvements	2,652,127
Hamilton Oaks Associates LLC Residential Apartments Brockton, Massachusetts
Real estate and accumulated depreciation
Encumbrances (First Mortgages)	26,666,000
Initial Cost to Partnerships
Land	2,175,000
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	3,935,300
Gross Amount at Which Carried at Close of Period
Land	2,175,000
Building Improvements	16,260,300
Totals	18,435,300
Accumulated Depreciation	12,488,092
Hamilton Oaks Associates LLC Residential Apartments Brockton, Massachusetts | Buildings and improvements
Initial Cost to Partnerships
Building Improvements	12,325,000
Highland Street Apartments, L.P. Residential Apartments Lowell, Massachusetts
Real estate and accumulated depreciation
Encumbrances (First Mortgages)	3,960,000
Initial Cost to Partnerships
Land	156,000
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	390,383
Gross Amount at Which Carried at Close of Period
Land	156,000
Building Improvements	1,024,468
Totals	1,180,468
Accumulated Depreciation	772,127
Highland Street Apartments, L.P. Residential Apartments Lowell, Massachusetts | Buildings and improvements
Initial Cost to Partnerships
Building Improvements	634,085
Linhart L.P. Residential/Commercial Newton, Massachusetts
Initial Cost to Partnerships
Land	385,000
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	1,817,632
Gross Amount at Which Carried at Close of Period
Land	385,000
Building Improvements	3,357,632
Totals	3,742,632
Accumulated Depreciation	2,752,397
Linhart L.P. Residential/Commercial Newton, Massachusetts | Buildings and improvements
Initial Cost to Partnerships
Building Improvements	1,540,000
Mill Street Gardens Residential Apartments Woburn Massachusetts
Real estate and accumulated depreciation
Encumbrances (First Mortgages)	31,000,000
Initial Cost to Partnerships
Land	9,798,478
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	2,702,946
Gross Amount at Which Carried at Close of Period
Land	9,798,478
Building Improvements	46,271,858
Totals	56,070,336
Accumulated Depreciation	5,828,719
Mill Street Gardens Residential Apartments Woburn Massachusetts | Buildings and improvements
Initial Cost to Partnerships
Building Improvements	43,568,912
Mill Street Development Woburn Massachusetts
Initial Cost to Partnerships
Land	1,375,000
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	17,280
Gross Amount at Which Carried at Close of Period
Land	1,375,000
Building Improvements	1,142,280
Totals	2,517,280
Accumulated Depreciation	83,090
Mill Street Development Woburn Massachusetts | Buildings and improvements
Initial Cost to Partnerships
Building Improvements	1,125,000
NERA Dean St. Associates LLC Residential Apartments Norwood, Massachusetts
Real estate and accumulated depreciation
Encumbrances (First Mortgages)	5,687,000
Initial Cost to Partnerships
Land	1,512,000
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	1,274,463
Gross Amount at Which Carried at Close of Period
Land	1,512,000
Building Improvements	6,975,943
Totals	8,487,943
Accumulated Depreciation	4,819,975
NERA Dean St. Associates LLC Residential Apartments Norwood, Massachusetts | Buildings and improvements
Initial Cost to Partnerships
Building Improvements	5,701,480
North Beacon 140 L.P. Residential Units Boston, Massachusetts
Real estate and accumulated depreciation
Encumbrances (First Mortgages)	12,683,000
Initial Cost to Partnerships
Land	936,000
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	2,538,548
Gross Amount at Which Carried at Close of Period
Land	936,000
Building Improvements	6,300,561
Totals	7,236,561
Accumulated Depreciation	5,450,762
North Beacon 140 L.P. Residential Units Boston, Massachusetts | Buildings and improvements
Initial Cost to Partnerships
Building Improvements	3,762,013
Olde English Apartments L.P. Residential Apartments Lowell, Massachusetts
Real estate and accumulated depreciation
Encumbrances (First Mortgages)	9,608,000
Initial Cost to Partnerships
Land	46,181
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	1,057,115
Gross Amount at Which Carried at Close of Period
Land	46,181
Building Improvements	1,935,438
Totals	1,981,619
Accumulated Depreciation	1,395,205
Olde English Apartments L.P. Residential Apartments Lowell, Massachusetts | Buildings and improvements
Initial Cost to Partnerships
Building Improvements	878,323
Redwood Hills L.P. Residential Units Worcester, Massachusetts
Real estate and accumulated depreciation
Encumbrances (First Mortgages)	17,105,000
Initial Cost to Partnerships
Land	1,200,000
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	5,188,284
Gross Amount at Which Carried at Close of Period
Land	1,200,000
Building Improvements	9,998,888
Totals	11,198,888
Accumulated Depreciation	7,292,620
Redwood Hills L.P. Residential Units Worcester, Massachusetts | Buildings and improvements
Initial Cost to Partnerships
Building Improvements	4,810,604
Residences at CaptainParkers LLC Residential Apartments Lexington, Massachusetts
Real estate and accumulated depreciation
Encumbrances (First Mortgages)	20,750,000
Initial Cost to Partnerships
Land	6,247,153
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	545,146
Gross Amount at Which Carried at Close of Period
Land	6,247,153
Building Improvements	25,499,923
Totals	31,747,076
Accumulated Depreciation	6,969,892
Residences at CaptainParkers LLC Residential Apartments Lexington, Massachusetts | Buildings and improvements
Initial Cost to Partnerships
Building Improvements	24,954,777
River Drive L.P. Residential Apartments Danvers, Massachusetts
Real estate and accumulated depreciation
Encumbrances (First Mortgages)	9,543,000
Initial Cost to Partnerships
Land	72,525
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	1,061,129
Gross Amount at Which Carried at Close of Period
Land	72,525
Building Improvements	1,648,906
Totals	1,721,431
Accumulated Depreciation	1,018,631
River Drive L.P. Residential Apartments Danvers, Massachusetts | Buildings and improvements
Initial Cost to Partnerships
Building Improvements	587,777
Riverside Apartments Condominium Units Massachusetts
Initial Cost to Partnerships
Land	23,346
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	146,281
Gross Amount at Which Carried at Close of Period
Land	23,346
Building Improvements	337,088
Totals	360,434
Accumulated Depreciation	265,663
Riverside Apartments Condominium Units Massachusetts | Buildings and improvements
Initial Cost to Partnerships
Building Improvements	190,807
School St Assoc LLC Residential Apartments Framingham, Massachusetts
Real estate and accumulated depreciation
Encumbrances (First Mortgages)	13,343,384
Initial Cost to Partnerships
Land	4,686,728
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	(327,390)
Gross Amount at Which Carried at Close of Period
Land	4,686,728
Building Improvements	18,419,521
Totals	23,106,249
Accumulated Depreciation	11,938,523
School St Assoc LLC Residential Apartments Framingham, Massachusetts | Buildings and improvements
Initial Cost to Partnerships
Building Improvements	18,746,911
WRF Associates LLC Strip Mall Framingham, Massachusetts
Real estate and accumulated depreciation
Encumbrances (First Mortgages)	6,017,073
Initial Cost to Partnerships
Land	3,280,000
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	81,477
Gross Amount at Which Carried at Close of Period
Land	3,280,000
Building Improvements	5,001,477
Totals	8,281,477
Accumulated Depreciation	3,737,621
WRF Associates LLC Strip Mall Framingham, Massachusetts | Buildings and improvements
Initial Cost to Partnerships
Building Improvements	4,920,000
WCB Associates LLC Residential Apartments Brockton, Massachusetts
Real estate and accumulated depreciation
Encumbrances (First Mortgages)	19,266,000
Initial Cost to Partnerships
Land	1,335,000
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	2,439,034
Gross Amount at Which Carried at Close of Period
Land	1,335,000
Building Improvements	10,004,535
Totals	11,339,535
Accumulated Depreciation	7,717,406
WCB Associates LLC Residential Apartments Brockton, Massachusetts | Buildings and improvements
Initial Cost to Partnerships
Building Improvements	7,565,501
Westgate Apartments Residential Units Burlington Massachusetts Member
Real estate and accumulated depreciation
Encumbrances (First Mortgages)	2,500,000
Initial Cost to Partnerships
Land	44,965
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	289,967
Gross Amount at Which Carried at Close of Period
Land	44,965
Building Improvements	4,768,654
Totals	4,813,619
Accumulated Depreciation	3,042,020
Westgate Apartments Residential Units Burlington Massachusetts Member | Buildings and improvements
Initial Cost to Partnerships
Building Improvements	4,478,687
Westgate Apartments LLC Residential Apartments Woburn, Massachusetts
Real estate and accumulated depreciation
Encumbrances (First Mortgages)	15,700,000
Initial Cost to Partnerships
Land	461,300
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	6,523,940
Gross Amount at Which Carried at Close of Period
Land	461,300
Building Improvements	8,948,576
Totals	9,409,876
Accumulated Depreciation	6,059,988
Westgate Apartments LLC Residential Apartments Woburn, Massachusetts | Buildings and improvements
Initial Cost to Partnerships
Building Improvements	2,424,636
Woodland Park Apartments LLC Newton Massachusetts
Real estate and accumulated depreciation
Encumbrances (First Mortgages)	22,250,000
Initial Cost to Partnerships
Land	9,114,334
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	1,137,070
Gross Amount at Which Carried at Close of Period
Land	9,114,334
Building Improvements	37,012,064
Totals	46,126,398
Accumulated Depreciation	9,440,214
Woodland Park Apartments LLC Newton Massachusetts | Buildings and improvements
Initial Cost to Partnerships
Building Improvements	$ 35,874,994