SUBSEQUENT EVENTS (Details) (USD $)	6 Months Ended		70 Months Ended					6 Months Ended		70 Months Ended	3 Months Ended	6 Months Ended		70 Months Ended	3 Months Ended	6 Months Ended		70 Months Ended	1 Months Ended		0 Months Ended	1 Months Ended	0 Months Ended	1 Months Ended	0 Months Ended	1 Months Ended	0 Months Ended	1 Months Ended	0 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Hamilton Bay Unit Sales item	Jun. 30, 2012 Hamilton Bay Unit Sales item	Apr. 30, 2008 Hamilton Bay Unit Sales item	Jun. 30, 2013 Class A units	Jun. 30, 2012 Class A units	Jun. 30, 2013 Class A units	Jun. 30, 2013 Class B Units	Jun. 30, 2013 Class B Units	Jun. 30, 2012 Class B Units	Jun. 30, 2013 Class B Units	Jun. 30, 2013 General Partnership units	Jun. 30, 2013 General Partnership units	Jun. 30, 2012 General Partnership units	Jun. 30, 2013 General Partnership units	Apr. 30, 2008 Mortgage Hamilton Bay Unit Sales	Jun. 30, 2013 Mortgage Hamilton Bay Unit Sales	Aug. 09, 2013 Subsequent events	Aug. 09, 2013 Subsequent events	Aug. 09, 2013 Subsequent events Class A units	Aug. 09, 2013 Subsequent events Class A units	Aug. 09, 2013 Subsequent events Class B Units	Aug. 09, 2013 Subsequent events Class B Units	Aug. 09, 2013 Subsequent events General Partnership units	Aug. 09, 2013 Subsequent events General Partnership units	Aug. 01, 2013 Subsequent events Mortgage Hamilton Bay Unit Sales	Jul. 07, 2013 Subsequent events Boylston Downtown LP Mortgage	Jul. 15, 2013 Subsequent events Hamilton Green Apartments, LLC item	Jul. 15, 2013 Subsequent events Hamilton Green Apartments, LLC Mortgage
Subsequent events
Amount of new loan																			$ 2,368,000											$ 40,000,000
Interest rate (as a percent)																			5.75%											3.97%
Period for which the entity is required to make interest only payments																														3 years
Amortization period of debt																														30 years
Amount of loan proceeds utilized for pay off the existing mortgage																														19,500,000
Outstanding amount of mortgage loan	131,671,632		131,671,632	138,055,522	1,668,000	1,668,000														1,668,000									1,318,000	20,000,000
Number of units					120	120	20																								193
Purchase price of real estate properties																															62,500,000
Short term finance for real estate properties																															40,000,000
Use of funds for real estate properties from exchange of apartments and cash reserves																															2,100,000
Basis of interest rate																																LIBOR
Notional margin over basis of interest rate (as a percent)																																2.25%
Current interest rate (as a percent)																																2.45%
Repayment of loan																													350,000
Contribution required to repay the debt																													800,000
Repurchase of depository receipts (in shares)			1,229,636					9,709		1,229,636	0	77		1,998	0	4		105			12,000	12,000
Repurchase price of depository receipts (in dollars per share)			$ 24.68																		$ 41.50	$ 41.50
Repurchase price of units (in dollars per share)										$ 740.40				$ 627.53				$ 627.53					$ 1,245.00	$ 1,245.00	$ 95	$ 95	$ 5	$ 5
Total cost of repurchase	$ 399,487	$ 69,379	$ 31,786,000					$ 321,240	$ 55,778			$ 74,335	$ 12,921			$ 3,912	$ 680				$ 498,000	$ 498,000			$ 118,275	$ 118,275	$ 6,225	$ 6,225