COMMITMENTS AND CONTINGENCIES, Development, Expansion and Renovation Projects and Pending Dispositions (Details)		3 Months Ended		9 Months Ended
		Jan. 31, 2016 USD ($) ft² shares Unit	Jan. 31, 2015 USD ($)	Jan. 31, 2016 USD ($) ft² shares Property Unit	Jan. 31, 2015 USD ($)
Real Estate Properties [Line Items]
Anticipated total cost	[1]	$ 178,190,000		$ 178,190,000
Project costs incurred to date	[1]	156,955,000		156,955,000
Construction interest capitalized		1,000,000	$ 1,400,000	4,400,000	$ 3,600,000
Deer Ridge - Jamestown, ND [Member]
Real Estate Properties [Line Items]
Project costs incurred to date		14,300,000		14,300,000
Cardinal Point, Grand Forks, ND [Member]
Real Estate Properties [Line Items]
Project costs incurred to date		23,000,000		23,000,000
71 France - Edina MN [Member]
Real Estate Properties [Line Items]
Project costs incurred to date		41,300,000		41,300,000
Other [Member]
Real Estate Properties [Line Items]
Project costs incurred to date	[1]	$ 3,524,000		$ 3,524,000
Multi-Family Residential [Member] | Deer Ridge - Jamestown, ND [Member]
Real Estate Properties [Line Items]
Number of apartment units | Unit		163		163
Anticipated total cost	[1]	$ 24,874,000		$ 24,874,000
Project costs incurred to date	[1]	$ 24,874,000		$ 24,874,000
Estimated quarter for completion				4
Estimated year for completion				2016
Multi-Family Residential [Member] | Cardinal Point, Grand Forks, ND [Member]
Real Estate Properties [Line Items]
Number of apartment units | Unit	[2]	251		251
Anticipated total cost	[1],[2]	$ 48,242,000		$ 48,242,000
Project costs incurred to date	[1],[2]	$ 48,242,000		$ 48,242,000
Estimated quarter for completion	[2]			4
Estimated year for completion	[2]			2016
Multi-Family Residential [Member] | 71 France - Edina MN [Member]
Real Estate Properties [Line Items]
Number of apartment units | Unit	[3]	241		241
Anticipated total cost	[1],[3]	$ 73,290,000		$ 73,290,000
Project costs incurred to date	[1],[3]	$ 69,105,000		$ 69,105,000
Estimated quarter for completion	[3]			1
Estimated year for completion	[3]			2017
Interest in joint venture		52.60%		52.60%
Area of real estate property | ft²		21,772		21,772
Multi-Family Residential [Member] | Monticello Crossings - Monticello, MN [Member]
Real Estate Properties [Line Items]
Number of apartment units | Unit		202		202
Anticipated total cost	[1]	$ 31,784,000		$ 31,784,000
Project costs incurred to date	[1]	$ 11,210,000		$ 11,210,000
Estimated quarter for completion				2
Estimated year for completion				2017
Multi-Family Residential [Member] | Rochester, Minnesota [Member]
Real Estate Properties [Line Items]
Number of properties pending acquisition | Property				4
Number of apartment units pending acquisition | shares		393		393
Purchase price of pending acquisition				$ 72,500,000
Cash to be paid for pending acquisition		$ 47,500,000		47,500,000
Value of limited partnership units to be issued in pending acquisition		$ 25,000,000		$ 25,000,000
Multi-Family Residential [Member] | St. Cloud, Minnesota [Member]
Real Estate Properties [Line Items]
Number of properties | Property				8
Sales price of pending disposition				$ 5,600,000
Unimproved Land [Member] | River Falls, Wisconsin [Member]
Real Estate Properties [Line Items]
Sales price of pending disposition				20,000
Healthcare [Member] | Omaha, Nebraska [Member]
Real Estate Properties [Line Items]
Sales price of pending disposition				$ 24,400,000

[1] Includes costs related to development projects that are placed in service in phases (Deer Ridge - $14.3 million, 71 France - $41.3 million, Cardinal Point - $23.0 million).

[2] Anticipated total cost as of January 31, 2016 includes incremental cost increase due to the replacement of the project's original general contractor. There may be additional costs for this project as it nears completion in the fourth quarter of fiscal year 2016.

[3] The project is being constructed in three phases by a joint venture entity in which we currently have an approximately 52.6% interest. The anticipated total cost amount given in the table above is the total cost to the joint venture entity. The anticipated total cost includes approximately 21,772 square feet of retail space.