COMMITMENTS AND CONTINGENCIES (Details) (USD $)	3 Months Ended			9 Months Ended
	Jan. 31, 2014 sqft		Jan. 31, 2013	Jan. 31, 2014 Units sqft		Jan. 31, 2013
Real Estate Properties [Line Items]
Number of properties subject to purchase options	14			14
Total property cost subject to purchase options	$ 113,400,000			$ 113,400,000
Total gross rental revenue from properties subject to purchase options				7,200,000
Number of properties subject to restrictions on taxable dispositions	110			110
Area of a real estate property (in square feet)	5,500,000			5,500,000
Number of apartment units placed in service				5,068
Real estate investment amount of properties (net of accumulated depreciation)	854,400,000			854,400,000
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	186,900,000		198,900,000	186,900,000		198,900,000
Joint ventures partner's interest acquired	0			0
Tenant Improvements	7,300,000			7,300,000
Commitment period for tenant improvements				12 months
Anticipated Total Cost	267,850,000			267,850,000
Project costs incurred to date	127,276,000			127,276,000
Construction interest capitalized	778,000		157,000	2,100,000		438,000
Bismarck, North Dakota [Member]
Real Estate Properties [Line Items]
Acre of land purchased (in acres)	35.0			35.0
Purchase price of pending acquisition	4,300,000			4,300,000
Brooklyn Park 7401 Boone Avenue, Brooklyn Park, Minnesota [Member]
Real Estate Properties [Line Items]
Acre of land purchased (in acres)	11.0			11.0
Purchase price of pending acquisition	2,500,000			2,500,000
Cardinal Point, Grand Forks, North Dakota [Member]
Real Estate Properties [Line Items]
Number of apartment units	251			251
Anticipated Total Cost	40,042,000			40,042,000
Project costs incurred to date	4,986,000			4,986,000
Estimated quarter for completion	4			4
Estimated year for completion	2015			2015
Cypress Court - St. Cloud, MN [Member]
Real Estate Properties [Line Items]
Number of apartment units	132	[1]		132	[1]
Anticipated Total Cost	14,322,000	[1]		14,322,000	[1]
Project costs incurred to date	13,583,000	[1]		13,583,000	[1]
Estimated quarter for completion	3	[1]		3	[1]
Estimated year for completion	2014	[1]		2014	[1]
Interest in joint venture held by joint venture partner (in hundredths)	86.00%	[1]		86.00%	[1]
Arcata Apartments, Golden Valley, Minnesota [Member]
Real Estate Properties [Line Items]
Number of apartment units	165			165
Anticipated Total Cost	33,151,000			33,151,000
Project costs incurred to date	9,250,000			9,250,000
Estimated quarter for completion	2			2
Estimated year for completion	2015			2015
Chateau II, Minot, North Dakota [Member]
Real Estate Properties [Line Items]
Number of apartment units	72	[2]		72	[2]
Anticipated Total Cost	14,711,000	[2]		14,711,000	[2]
Project costs incurred to date	1,741,000	[2]		1,741,000	[2]
Estimated quarter for completion	4	[2]		4	[2]
Estimated year for completion	2015	[2]		2015	[2]
Dakota Commons, Williston, North Dakota [Member]
Real Estate Properties [Line Items]
Number of apartment units	44			44
Anticipated Total Cost	10,736,000			10,736,000
Project costs incurred to date	6,139,000			6,139,000
Estimated quarter for completion	1			1
Estimated year for completion	2015			2015
Rapid City, South Dakota [Member]
Real Estate Properties [Line Items]
Number of buildings				2
Purchase price of pending acquisition	18,300,000			18,300,000
Cash paid for acquisition	6,000,000			6,000,000
Debt assumed in acquisition	12,300,000			12,300,000
Rapid City, South Dakota [Member] | Building One [Member]
Real Estate Properties [Line Items]
Number of apartment units	152			152
Rapid City, South Dakota [Member] | Building Two [Member]
Real Estate Properties [Line Items]
Number of apartment units	52			52
River Ridge - Bismarck, ND [Member]
Real Estate Properties [Line Items]
Number of apartment units	146	[3]		146	[3]
Anticipated Total Cost	25,863,000	[3]		25,863,000	[3]
Project costs incurred to date	24,818,000	[3]		24,818,000	[3]
Estimated quarter for completion	3	[3]		3	[3]
Estimated year for completion	2014	[3]		2014	[3]
RED 20 - Minneapolis, MN [Member]
Real Estate Properties [Line Items]
Area of property (square feet)	10,625	[4]		10,625	[4]
Number of apartment units	130	[4]		130	[4]
Anticipated Total Cost	29,462,000	[4]		29,462,000	[4]
Project costs incurred to date	9,333,000	[4]		9,333,000	[4]
Estimated quarter for completion	2	[4]		2	[4]
Estimated year for completion	2015	[4]		2015	[4]
Interest in joint venture held by joint venture partner (in hundredths)	58.60%	[4]		58.60%	[4]
Renaissance Heights I Apartments, Williston, North Dakota [Member]
Real Estate Properties [Line Items]
Number of apartment units	288	[5]		288	[5]
Anticipated Total Cost	62,362,000	[5]		62,362,000	[5]
Project costs incurred to date	33,934,000	[5]		33,934,000	[5]
Estimated quarter for completion	2	[5]		2	[5]
Estimated year for completion	2015	[5]		2015	[5]
Interest in joint venture held by joint venture partner (in hundredths)	70.00%	[5]		70.00%	[5]
The Commons at Southgate, Minot, North Dakota [Member]
Real Estate Properties [Line Items]
Number of apartment units	233	[6]		233	[6]
Anticipated Total Cost	37,201,000	[6]		37,201,000	[6]
Project costs incurred to date	23,492,000	[6]		23,492,000	[6]
Estimated quarter for completion	2	[6]		2	[6]
Estimated year for completion	2015	[6]		2015	[6]
Interest in joint venture held by joint venture partner (in hundredths)	51.00%	[6]		51.00%	[6]
vacant land in Rapid City, South Dakota [Member]
Real Estate Properties [Line Items]
Area of land (in acres)	10.8			10.8
Number of land				2
Purchase price of pending acquisition	$ 1,400,000			$ 1,400,000

[1] The project was substantially completed in the third quarter of the Company’s fiscal year 2014. The Company is an approximately 86% partner in the joint venture entity constructing this project; the anticipated total cost amount given is the total cost to the joint venture entity. The joint venture’s results are consolidated in the Company’s financial statements.

[2] On December 5, 2013, this development project was destroyed by fire. See Note 2 for additional information.

[3] The project was substantially completed in the third quarter of the Company’s fiscal year 2014.

[4] The Company is an approximately 58.6% partner in the joint venture entity constructing this project; the anticipated total cost amount given is the total cost to the joint venture entity. The joint venture’s results are consolidated in the Company’s financial statements.

[5] The Company is an approximately 70% partner in the joint venture entity constructing this project; the anticipated total cost amount given is the total cost to the joint venture entity. The joint venture’s results are consolidated in the Company’s financial statements.

[6] The Company is an approximately 51% partner in the joint venture entity constructing this project; the anticipated total cost amount given is the total cost to the joint venture entity. The joint venture’s results are consolidated in the Company’s financial statements.