RENTAL PROPERTIES - Real Estate Detail (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2012
Real estate and accumulated depreciation
Encumbrances (First Mortgages)	$ 214,134,191
Initial Cost to Partnerships
Land	48,020,919
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	71,885,536
Gross Amount at Which Carried at Close of Period
Land	47,308,182
Building Improvements	216,351,111
Totals	263,659,293	$ 261,276,898	$ 225,021,946	$ 221,454,286
Accumulated Depreciation	94,196,482	$ 84,579,584	$ 75,905,862	$ 68,549,625
Buildings and improvements
Initial Cost to Partnerships
Building Improvements	$ 174,998,961
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)	$ 39,767,081
Initial Cost to Partnerships
Land	2,112,000
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	8,465,020
Gross Amount at Which Carried at Close of Period
Land	2,112,000
Building Improvements	17,058,129
Totals	19,170,129
Accumulated Depreciation	11,367,310
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)	2,551,784
Initial Cost to Partnerships
Land	684,000
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	422,736
Gross Amount at Which Carried at Close of Period
Land	684,000
Building Improvements	3,538,736
Totals	4,222,736
Accumulated Depreciation	2,051,187
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	1,644,670
Gross Amount at Which Carried at Close of Period
Land	177,610
Building Improvements	3,123,029
Totals	3,300,639
Accumulated Depreciation	2,211,354
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	1,185,432
Gross Amount at Which Carried at Close of Period
Land	342,000
Building Improvements	2,553,101
Totals	2,895,101
Accumulated Depreciation	1,639,400
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	3,053,498
Gross Amount at Which Carried at Close of Period
Land	1,410,000
Building Improvements	8,718,314
Totals	10,128,314
Accumulated Depreciation	5,548,937
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	1,241,254
Gross Amount at Which Carried at Close of Period
Land	91,400
Building Improvements	1,981,614
Totals	2,073,014
Accumulated Depreciation	1,133,390
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)	4,556,929
Initial Cost to Partnerships
Land	1,341,737
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	(31,186)
Gross Amount at Which Carried at Close of Period
Land	1,341,737
Building Improvements	8,426,311
Totals	9,768,048
Accumulated Depreciation	1,950,071
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	267,785
Gross Amount at Which Carried at Close of Period
Land	2,362,596
Building Improvements	4,881,770
Totals	7,244,366
Accumulated Depreciation	1,290,268
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)	37,171,505
Initial Cost to Partnerships
Land	16,054,336
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	314,568
Gross Amount at Which Carried at Close of Period
Land	15,385,792
Building Improvements	45,777,550
Totals	61,163,342
Accumulated Depreciation	11,906,360
Hamilton Green Apartments Residential Apartments Andover, Massachusetts | Buildings and improvements
Initial Cost to Partnerships
Building Improvements	44,794,438
Hamilton Linewt LLC Commercial-1031 Exchange Newton, Massachusetts
Initial Cost to Partnerships
Land	884,042
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	62,608
Gross Amount at Which Carried at Close of Period
Land	884,042
Building Improvements	2,714,735
Totals	3,598,777
Accumulated Depreciation	635,673
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	3,066,647
Gross Amount at Which Carried at Close of Period
Land	2,175,000
Building Improvements	15,391,647
Totals	17,566,647
Accumulated Depreciation	9,225,149
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	296,725
Gross Amount at Which Carried at Close of Period
Land	156,000
Building Improvements	930,810
Totals	1,086,810
Accumulated Depreciation	630,619
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	1,467,584
Gross Amount at Which Carried at Close of Period
Land	385,000
Building Improvements	3,007,584
Totals	3,392,584
Accumulated Depreciation	2,148,185
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	1,066,249
Gross Amount at Which Carried at Close of Period
Land	1,512,000
Building Improvements	6,767,729
Totals	8,279,729
Accumulated Depreciation	3,420,061
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	2,336,390
Gross Amount at Which Carried at Close of Period
Land	936,000
Building Improvements	6,098,403
Totals	7,034,403
Accumulated Depreciation	4,020,053
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	1,222,733
Gross Amount at Which Carried at Close of Period
Land	46,181
Building Improvements	2,101,056
Totals	2,147,237
Accumulated Depreciation	1,391,338
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	3,367,174
Gross Amount at Which Carried at Close of Period
Land	1,200,000
Building Improvements	8,177,778
Totals	9,377,778
Accumulated Depreciation	5,135,322
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	31,924,288
Gross Amount at Which Carried at Close of Period
Land	6,247,153
Building Improvements	25,677,135
Totals	31,924,288
Accumulated Depreciation	1,749,091
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	1,026,791
Gross Amount at Which Carried at Close of Period
Land	72,525
Building Improvements	1,614,568
Totals	1,687,093
Accumulated Depreciation	816,449
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	67,767
Gross Amount at Which Carried at Close of Period
Land	23,346
Building Improvements	258,574
Totals	281,920
Accumulated Depreciation	213,902
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)	14,823,892
Initial Cost to Partnerships
Land	4,686,728
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	(928,816)
Gross Amount at Which Carried at Close of Period
Land	4,686,728
Building Improvements	17,818,095
Totals	22,504,824
Accumulated Depreciation	8,700,765
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)	6,000,000
Initial Cost to Partnerships
Land	3,280,000
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	86,202
Gross Amount at Which Carried at Close of Period
Land	3,280,000
Building Improvements	5,006,202
Totals	8,286,202
Accumulated Depreciation	2,903,034
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	2,038,505
Gross Amount at Which Carried at Close of Period
Land	1,335,000
Building Improvements	9,604,006
Totals	10,939,006
Accumulated Depreciation	5,689,418
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	238,184
Gross Amount at Which Carried at Close of Period
Land	44,965
Building Improvements	4,716,871
Totals	4,761,836
Accumulated Depreciation	2,155,051
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	7,982,728
Gross Amount at Which Carried at Close of Period
Land	417,107
Building Improvements	10,407,364
Totals	10,824,471
Accumulated Depreciation	6,264,096
Westgate Apartments LLC Residential Apartments Woburn, Massachusetts | Buildings and improvements
Initial Cost to Partnerships
Building Improvements	$ 2,424,636