COMMITMENTS AND CONTINGENCIES (Details) (USD $)	3 Months Ended		6 Months Ended					6 Months Ended															6 Months Ended				6 Months Ended
	Oct. 31, 2013 sqft	Oct. 31, 2012	Oct. 31, 2013 Unit sqft	Oct. 31, 2012	Oct. 31, 2013 Anoka, Minnesota [Member]	Oct. 31, 2013 Burnsville, Minnesota [Member]	Oct. 31, 2013 Cardinal Point, Grand Forks, North Dakota [Member] Unit	Oct. 31, 2013 Clive, Iowa [Member]	Oct. 31, 2013 Cypress Court - St. Cloud, MN [Member] Building Unit	Oct. 31, 2013 Arcata Apartments, Golden Valley, Minnesota [Member] acre Unit	Oct. 31, 2013 Chateau II, Minot, North Dakota [Member] Building Unit	Apr. 30, 2012 Chateau II, Minot, North Dakota [Member] Unit	Oct. 31, 2013 Chateau II, Minot, North Dakota [Member] Building One [Member] Unit	Oct. 31, 2013 Chateau II, Minot, North Dakota [Member] Building Two [Member] Unit	Oct. 31, 2013 Dakota Commons, Williston, North Dakota [Member] Unit	Oct. 31, 2013 Monticello, Minnesota [Member] acre	Oct. 31, 2013 Rapid City, South Dakota [Member] acre	Oct. 31, 2013 River Ridge, Bismarck, ND [Member] Unit	Oct. 31, 2013 RED 20 - Minneapolis, MN [Member] Unit sqft	Oct. 31, 2013 Renaissance Heights I Apartments, Williston, North Dakota [Member] acre Unit	Oct. 31, 2013 Renaissance Heights I Apartments, Williston, North Dakota [Member] Project Phase One [Member] Unit	Oct. 31, 2013 Renaissance Heights I Apartments, Williston, North Dakota [Member] Project Phases Two and Three [Member] Unit	Oct. 31, 2013 Sioux Falls, South Dakota [Member]	Oct. 31, 2013 Southgate, Minot, North Dakota [Member] Unit	Oct. 31, 2013 The Landing at Southgate, Minot, ND [Member] Unit	Oct. 31, 2013 The Commons at Southgate, Minot, North Dakota [Member] Unit	Oct. 31, 2013 Winsted, Minnesota [Member]
Real Estate Properties [Line Items]
Number of properties subject to purchase options	15		15
Total property cost subject to purchase options	$ 114,900,000		$ 114,900,000
Total gross rental revenue from properties subject to purchase options			4,800,000
Number of properties subject to restrictions on taxable dispositions	114		114
Area of a real estate property (in square feet)	5,900,000		5,900,000
Number of apartment units placed in service			5,068
Real estate investment amount of properties (net of accumulated depreciation)	876,000,000		876,000,000
Redemption basis	one-for-one		one-for-one
Redemption holding period, minimum			1 year
Number of consecutive trading days for valuation			10 days
Aggregate redemption value of UPREIT Units of operating partnership owned by limited partners	194,100,000	177,800,000	194,100,000	177,800,000
Joint ventures partner's interest acquired	0		0
Tenant Improvements	10,100,000		10,100,000
Commitment period for tenant improvements			12 months
Area of property (square feet)																			10,000
Area of land (in acres)										2						5.0	10.8			14.5
Acre of land purchased (in acres)																				40
Number of apartment units							251		132	165	72	32	15	57	44			146	130	750	288	462		341	36	233
Number of certificate of occupancy units																		60
Number of buildings									2		2														3
Land purchased							1,600,000			2,100,000					823,000
Estimated cost of project							40,000,000		14,300,000	34,400,000	14,700,000				10,700,000			25,900,000	29,500,000	62,400,000					15,800,000	36,400,000
Project costs incurred to date							4,500,000		13,500,000	5,900,000	6,500,000							23,500,000	5,900,000	26,900,000					15,100,000	17,200,000
Interest in joint venture (in hundredths)									79.00%										58.60%	70.00%				51.00%
Interest in joint venture held by joint venture partner (in hundredths)									21.00%										41.40%					49.00%
Construction interest capitalized	781,000	120,000	1,400,000	281,000
Purchase price of pending acquisition																656,000	1,400,000
Sales price of property pending disposition					$ 325,000	$ 650,000		$ 2,700,000															$ 3,500,000				$ 725,000