RENTAL PROPERTIES (Real estate) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Gross Amount at Which Carried at Close of Period
Totals	$ 261,276,898	$ 225,021,946	$ 221,454,286	$ 158,624,893
Accumulated Depreciation	$ 84,579,584	$ 75,905,862	$ 68,549,625	$ 63,651,293
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	39 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)	$ 40,000,000
Initial Cost to Partnerships
Land	2,112,000
Building Improvements	8,593,109
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	8,192,079
Gross Amount at Which Carried at Close of Period
Land	2,112,000
Building Improvements	16,785,188
Totals	18,897,188
Accumulated Depreciation	10,755,089
Brookside Associates LLC Residential Apartments Woburn, Massachusetts
Real estate and accumulated depreciation
Encumbrances (First Mortgages)	2,598,337
Initial Cost to Partnerships
Land	684,000
Building Improvements	3,116,000
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	432,302
Gross Amount at Which Carried at Close of Period
Land	684,000
Building Improvements	3,548,302
Totals	4,232,302
Accumulated Depreciation	1,945,022
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
Building Improvements	1,478,359
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	1,689,128
Gross Amount at Which Carried at Close of Period
Land	177,610
Building Improvements	3,167,487
Totals	3,345,097
Accumulated Depreciation	2,154,856
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
Building Improvements	1,367,669
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	1,196,696
Gross Amount at Which Carried at Close of Period
Land	342,000
Building Improvements	2,564,365
Totals	2,906,365
Accumulated Depreciation	1,532,004
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
Building Improvements	5,664,816
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	2,207,782
Gross Amount at Which Carried at Close of Period
Land	1,410,000
Building Improvements	7,872,598
Totals	9,282,598
Accumulated Depreciation	5,199,814
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
Building Improvements	740,360
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	1,226,670
Gross Amount at Which Carried at Close of Period
Land	91,400
Building Improvements	1,967,030
Totals	2,058,430
Accumulated Depreciation	1,062,137
Hamilton Battle Green LLC Residential Apartments Lexington, Massachusetts
Real estate and accumulated depreciation
Encumbrances (First Mortgages)	4,649,132
Initial Cost to Partnerships
Land	1,341,737
Building Improvements	8,457,497
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	170,445
Gross Amount at Which Carried at Close of Period
Land	1,341,737
Building Improvements	8,627,942
Totals	9,969,679
Accumulated Depreciation	1,823,135
Hamilton Cypress LLC Commercial-1031Exchange Brookline, Massachusetts
Initial Cost to Partnerships
Land	2,362,596
Building Improvements	4,613,985
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	259,375
Gross Amount at Which Carried at Close of Period
Land	2,362,596
Building Improvements	4,873,360
Totals	7,235,956
Accumulated Depreciation	1,085,242
Hamilton Green Apartments Residential Apartments Andover, Massachusetts
Real estate and accumulated depreciation
Encumbrances (First Mortgages)	38,500,000
Initial Cost to Partnerships
Land	16,054,336
Building Improvements	44,794,438
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	748,572
Gross Amount at Which Carried at Close of Period
Land	16,054,336
Building Improvements	45,543,010
Totals	61,597,346
Accumulated Depreciation	8,395,786
Hamilton Linewt LLC Commercial-1031 Exchange Newton, Massachusetts
Initial Cost to Partnerships
Land	884,042
Building Improvements	2,652,127
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	564,048
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
Building Improvements	12,325,000
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	2,574,848
Gross Amount at Which Carried at Close of Period
Land	2,175,000
Building Improvements	14,899,848
Totals	17,074,848
Accumulated Depreciation	8,580,806
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
Building Improvements	634,085
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	338,724
Gross Amount at Which Carried at Close of Period
Land	156,000
Building Improvements	972,809
Totals	1,128,809
Accumulated Depreciation	635,675
Linhart L.P. Residential/Commercial Newton, Massachusetts
Initial Cost to Partnerships
Land	385,000
Building Improvements	1,540,000
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	1,331,870
Gross Amount at Which Carried at Close of Period
Land	385,000
Building Improvements	2,871,870
Totals	3,256,870
Accumulated Depreciation	2,047,890
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
Building Improvements	5,701,480
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	961,065
Gross Amount at Which Carried at Close of Period
Land	1,512,000
Building Improvements	6,662,545
Totals	8,174,545
Accumulated Depreciation	3,143,032
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
Building Improvements	3,762,013
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	2,158,122
Gross Amount at Which Carried at Close of Period
Land	936,000
Building Improvements	5,920,135
Totals	6,856,135
Accumulated Depreciation	3,743,872
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
Building Improvements	878,323
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	1,262,126
Gross Amount at Which Carried at Close of Period
Land	46,181
Building Improvements	2,140,449
Totals	2,186,630
Accumulated Depreciation	1,386,246
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
Building Improvements	4,810,604
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	3,171,266
Gross Amount at Which Carried at Close of Period
Land	1,200,000
Building Improvements	7,981,870
Totals	9,181,870
Accumulated Depreciation	4,753,632
Residences at CaptainParkers LLC Residential Apartments Lexington, Massachusetts
Initial Cost to Partnerships
Land	6,247,153
Building Improvements	24,954,777
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	31,201,930
Gross Amount at Which Carried at Close of Period
Land	6,247,153
Building Improvements	24,954,777
Totals	31,201,930
Accumulated Depreciation	385,301
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
Building Improvements	587,777
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	1,130,773
Gross Amount at Which Carried at Close of Period
Land	72,525
Building Improvements	1,718,550
Totals	1,791,075
Accumulated Depreciation	847,593
Riverside Apartments Condominium Units Massachusetts
Initial Cost to Partnerships
Land	23,346
Building Improvements	190,807
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	54,973
Gross Amount at Which Carried at Close of Period
Land	23,346
Building Improvements	245,780
Totals	269,126
Accumulated Depreciation	205,387
School St Assoc LLC Residential Apartments Framingham, Massachusetts
Real estate and accumulated depreciation
Encumbrances (First Mortgages)	15,000,000
Initial Cost to Partnerships
Land	4,686,728
Building Improvements	18,746,911
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	(1,254,212)
Gross Amount at Which Carried at Close of Period
Land	4,686,728
Building Improvements	17,492,699
Totals	22,179,427
Accumulated Depreciation	7,958,005
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
Building Improvements	4,920,000
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	86,445
Gross Amount at Which Carried at Close of Period
Land	3,280,000
Building Improvements	5,006,445
Totals	8,286,445
Accumulated Depreciation	2,737,573
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
Building Improvements	7,565,501
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	1,722,213
Gross Amount at Which Carried at Close of Period
Land	1,335,000
Building Improvements	9,287,714
Totals	10,622,714
Accumulated Depreciation	5,303,172
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
Building Improvements	4,478,687
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	244,281
Gross Amount at Which Carried at Close of Period
Land	44,965
Building Improvements	4,722,968
Totals	4,767,933
Accumulated Depreciation	1,984,655
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
Building Improvements	2,424,636
Cost Capitalized Subsequent to Acquisition
Improvements, Net of retirements	8,333,060
Gross Amount at Which Carried at Close of Period
Land	417,107
Building Improvements	10,757,696
Totals	11,174,803
Accumulated Depreciation	$ 6,349,611