RENTAL PROPERTIES - Real Estate Detail (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Real estate and accumulated depreciation
Encumbrances (First Mortgages)	$ 253,711,194
Initial Cost to Partnerships
Land	63,950,775
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	35,815,591
Gross Amount at Which Carried at Close of Period
Land	63,950,775
Building Improvements	273,951,633
Totals	337,902,411	$ 311,951,597	$ 263,659,293	$ 261,276,898
Accumulated Depreciation	107,391,148	$ 104,797,803	$ 94,196,482	$ 84,579,584
Buildings and improvements
Initial Cost to Partnerships
Building Improvements	$ 238,136,042
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)	$ 38,303,055
Initial Cost to Partnerships
Land	2,112,000
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	9,092,105
Gross Amount at Which Carried at Close of Period
Land	2,112,000
Building Improvements	17,685,214
Totals	19,797,214
Accumulated Depreciation	$ 12,755,764
Estimated useful lives	3 years
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)	2,449,146
Initial Cost to Partnerships
Land	684,000
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	432,470
Gross Amount at Which Carried at Close of Period
Land	684,000
Building Improvements	3,548,470
Totals	4,232,470
Accumulated Depreciation	$ 2,303,052
Estimated useful lives	3 years
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)	4,160,000
Initial Cost to Partnerships
Land	177,610
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	1,643,458
Gross Amount at Which Carried at Close of Period
Land	177,610
Building Improvements	3,121,817
Totals	3,299,427
Accumulated Depreciation	$ 2,289,823
Estimated useful lives	3 years
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)	3,750,000
Initial Cost to Partnerships
Land	342,000
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	1,151,109
Gross Amount at Which Carried at Close of Period
Land	342,000
Building Improvements	2,518,778
Totals	2,860,778
Accumulated Depreciation	$ 1,872,703
Estimated useful lives	3 years
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)	14,780,000
Initial Cost to Partnerships
Land	1,410,000
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	4,016,797
Gross Amount at Which Carried at Close of Period
Land	1,410,000
Building Improvements	9,681,613
Totals	11,091,613
Accumulated Depreciation	$ 6,313,509
Estimated useful lives	3 years
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)	2,415,000
Initial Cost to Partnerships
Land	91,400
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	1,361,625
Gross Amount at Which Carried at Close of Period
Land	91,400
Building Improvements	2,101,985
Totals	2,193,385
Accumulated Depreciation	$ 1,304,598
Estimated useful lives	3 years
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)	4,358,279
Initial Cost to Partnerships
Land	1,341,737
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	135,799
Gross Amount at Which Carried at Close of Period
Land	1,341,737
Building Improvements	8,593,296
Totals	9,935,033
Accumulated Depreciation	$ 2,635,081
Estimated useful lives	3 years
Hamilton Battle Green LLC Residential Apartments Lexington, Massachusetts | Buildings and improvements
Initial Cost to Partnerships
Building Improvements	$ 8,457,497
Hamilton Cypress LLC Commercial-1031 Exchange Brookline, Massachusetts
Initial Cost to Partnerships
Land	2,362,596
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	36,319
Gross Amount at Which Carried at Close of Period
Land	2,362,596
Building Improvements	4,650,304
Totals	7,012,900
Accumulated Depreciation	$ 1,423,342
Estimated useful lives	3 years
Hamilton Cypress LLC Commercial-1031 Exchange 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)	35,910,042
Initial Cost to Partnerships
Land	16,054,336
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	(8,265,823)
Gross Amount at Which Carried at Close of Period
Land	16,054,336
Building Improvements	36,528,615
Totals	52,582,951
Accumulated Depreciation	$ 9,142,815
Estimated useful lives	3 years
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)	20,829,315
Initial Cost to Partnerships
Land	6,815,522
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	302,384
Gross Amount at Which Carried at Close of Period
Land	6,815,522
Building Improvements	27,564,471
Totals	34,379,993
Accumulated Depreciation	$ 1,248,735
Estimated useful lives	3 years
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	138,904
Gross Amount at Which Carried at Close of Period
Land	884,042
Building Improvements	2,791,031
Totals	3,675,073
Accumulated Depreciation	$ 780,407
Estimated useful lives	3 years
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)	11,925,000
Initial Cost to Partnerships
Land	2,175,000
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	3,316,818
Gross Amount at Which Carried at Close of Period
Land	2,175,000
Building Improvements	15,641,818
Totals	17,816,818
Accumulated Depreciation	$ 10,333,004
Estimated useful lives	3 years
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)	1,050,000
Initial Cost to Partnerships
Land	156,000
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	344,651
Gross Amount at Which Carried at Close of Period
Land	156,000
Building Improvements	978,736
Totals	1,134,736
Accumulated Depreciation	$ 662,712
Estimated useful lives	3 years
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	1,608,452
Gross Amount at Which Carried at Close of Period
Land	385,000
Building Improvements	3,148,452
Totals	3,533,452
Accumulated Depreciation	$ 2,364,279
Estimated useful lives	3 years
Linhart L.P. Residential/Commercial Newton, Massachusetts | Buildings and improvements
Initial Cost to Partnerships
Building Improvements	$ 1,540,000
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	1,077,782
Gross Amount at Which Carried at Close of Period
Land	1,512,000
Building Improvements	6,779,262
Totals	8,291,262
Accumulated Depreciation	$ 3,963,672
Estimated useful lives	3 years
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)	6,937,000
Initial Cost to Partnerships
Land	936,000
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	2,385,904
Gross Amount at Which Carried at Close of Period
Land	936,000
Building Improvements	6,147,917
Totals	7,083,917
Accumulated Depreciation	$ 4,568,754
Estimated useful lives	3 years
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)	3,080,000
Initial Cost to Partnerships
Land	46,181
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	951,975
Gross Amount at Which Carried at Close of Period
Land	46,181
Building Improvements	1,830,298
Totals	1,876,479
Accumulated Depreciation	$ 1,275,870
Estimated useful lives	3 years
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)	6,743,000
Initial Cost to Partnerships
Land	1,200,000
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	4,582,731
Gross Amount at Which Carried at Close of Period
Land	1,200,000
Building Improvements	9,393,335
Totals	10,593,335
Accumulated Depreciation	$ 6,018,415
Estimated useful lives	3 years
Redwood Hills L.P. Residential Units Worcester, Massachusetts | Buildings and improvements
Initial Cost to Partnerships
Building Improvements	$ 4,810,604
Residences at Captain Parkers LLC Residential Apartments Lexington, Massachusetts
Real estate and accumulated depreciation
Encumbrances (First Mortgages)	20,071,000
Initial Cost to Partnerships
Land	6,247,153
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	1,136,881
Gross Amount at Which Carried at Close of Period
Land	6,247,153
Building Improvements	26,091,658
Totals	32,338,811
Accumulated Depreciation	$ 4,591,926
Estimated useful lives	3 years
Residences at Captain Parkers 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)	3,465,000
Initial Cost to Partnerships
Land	72,525
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	978,012
Gross Amount at Which Carried at Close of Period
Land	72,525
Building Improvements	1,565,789
Totals	1,638,314
Accumulated Depreciation	$ 841,906
Estimated useful lives	3 years
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	89,693
Gross Amount at Which Carried at Close of Period
Land	23,346
Building Improvements	280,500
Totals	303,846
Accumulated Depreciation	$ 236,775
Estimated useful lives	3 years
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)	14,264,674
Initial Cost to Partnerships
Land	4,686,728
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	(591,809)
Gross Amount at Which Carried at Close of Period
Land	4,686,728
Building Improvements	18,155,102
Totals	22,841,830
Accumulated Depreciation	$ 9,786,476
Estimated useful lives	3 years
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)	6,083,683
Initial Cost to Partnerships
Land	3,280,000
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	72,337
Gross Amount at Which Carried at Close of Period
Land	3,280,000
Building Improvements	4,992,337
Totals	8,272,337
Accumulated Depreciation	$ 3,230,828
Estimated useful lives	3 years
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)	7,000,000
Initial Cost to Partnerships
Land	1,335,000
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	2,420,595
Gross Amount at Which Carried at Close of Period
Land	1,335,000
Building Improvements	9,986,096
Totals	11,321,096
Accumulated Depreciation	$ 6,567,275
Estimated useful lives	3 years
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	247,604
Gross Amount at Which Carried at Close of Period
Land	44,965
Building Improvements	4,726,291
Totals	4,771,256
Accumulated Depreciation	$ 2,503,776
Estimated useful lives	3 years
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	6,378,400
Gross Amount at Which Carried at Close of Period
Land	461,300
Building Improvements	8,803,036
Totals	9,264,336
Accumulated Depreciation	$ 5,277,436
Estimated useful lives	3 years
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	770,418
Gross Amount at Which Carried at Close of Period
Land	9,114,334
Building Improvements	36,645,412
Totals	45,759,746
Accumulated Depreciation	$ 3,098,215
Estimated useful lives	3 years
Woodland Park Apartments LLC Newton Massachusetts | Buildings and improvements
Initial Cost to Partnerships
Building Improvements	$ 35,874,994