COMMITMENTS AND CONTINGENCIES (Details) (USD $)	3 Months Ended
	Jul. 31, 2012	Jul. 31, 2011	Jan. 31, 2012
Real Estate Properties [Line Items]
Number of properties subject to purchase options	17
Total property cost subject to purchase options	$ 114,100,000
Total gross rental revenue from properties subject to purchase options	2,400,000
Number of properties subject to restrictions on taxable dispositions	110
Real estate investment amount of properties (net of accumulated depreciation)	822,300,000
Redemption basis	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	172,400,000	164,000,000
Joint ventures partner's interest acquired			1,300,000
Tenant Improvements	6,600,000
Commitment period for tenant improvements	12 months
Construction interest capitalized	161,000	75,000
Multi-Family Conversion, Minot, North Dakota [Member]
Real Estate Properties [Line Items]
Area of a real estate property (in square feet)	15,000
Number of apartment units	20
Estimated cost of construction	3,000,000
Project costs incurred to date	647,000
Quarry Ridge Apartment Homes, Rochester, Minnesota [Member]
Real Estate Properties [Line Items]
Number of apartment units	159
Estimated cost of construction	17,300,000
Project costs incurred to date	15,600,000
Williston Apartments, Williston, North Dakota [Member]
Real Estate Properties [Line Items]
Number of apartment units	145
Estimated cost of construction	19,500,000
Interest in joint venture (in hundredths)	60.00%
Interest in joint venture held by joint venture partner (in hundredths)	40.00%
Cash contribution to project	3,300,000
Joint venture partner contribution	2,200,000
Project costs incurred to date	17,800,000
Senior Housing Memory Care and Assisted Living Units, Laramie, Wyoming [Member]
Real Estate Properties [Line Items]
Number of apartment units	48
Number of assisted living units	61
Number of memory care units	16
Number of assisted living units to be converted to memory care units	16
Number of additional assisted living units	29
Estimated cost of construction	3,800,000
Project costs incurred to date	3,100,000
Industrial-Office Build-to-Suit, Minot, North Dakota [Member]
Real Estate Properties [Line Items]
Area of land (in acres)	9.6
Area of a real estate property (in square feet)	28,000
Estimated cost of construction	5,800,000
Project costs incurred to date	3,600,000
Jamestown Medical Office Building, Jamestown, North Dakota [Member]
Real Estate Properties [Line Items]
Area of land (in acres)	4.9
Area of a real estate property (in square feet)	45,000
Estimated cost of construction	3,000,000
Interest in joint venture (in hundredths)	51.00%
Cash contribution to project	1,500,000
Project costs incurred to date	9,200,000
Number of storey building	1
Lease term of property	79 years
Number of renewal of lease	2
Renewal of lease	10 years
Proceeds from construction loan	6,200,000
Branch Bank Building, Minot, North Dakota [Member]
Real Estate Properties [Line Items]
Area of a real estate property (in square feet)	3,700
Estimated cost of construction	75,000
Project costs incurred to date	$ 1,700,000
Lease term of property	20 years
Combined Commercial Segments [Member]
Real Estate Properties [Line Items]
Area of a real estate property (in square feet)	6,100,000
Multi Family Residential [Member]
Real Estate Properties [Line Items]
Number of apartment units	4,522