ACQUISITIONS, DEVELOPMENTS PLACED IN SERVICE AND DISPOSITIONS, PROPERTY DISPOSITIONS (Details) $ in Thousands		3 Months Ended		6 Months Ended
		Oct. 31, 2015 USD ($) ft² Property	Oct. 31, 2014 USD ($) ft² Property Unit	Oct. 31, 2015 USD ($) ft² Property	Oct. 31, 2014 USD ($) ft² Unit
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sales Price		$ 371,900	$ 10,900	$ 378,860	$ 17,576
Book Value and Sales Cost				355,127	19,320
Gain/(Loss)				$ 23,733	$ (1,744)
Kalispell Unimproved - Kalispell, MT [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Date Disposed					Oct. 15, 2014
Sales Price					$ 670
Book Value and Sales Cost					670
Gain/(Loss)					$ 0
Office Properties [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties sold | Property		39	1	39
Retail Properties [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties sold | Property		15	1	15
Healthcare Properties [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties sold | Property		1		1
Multifamily [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties sold | Property			1
Multifamily [Member] | 83 unit - Lancaster - St. Cloud, MN [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Date Disposed					Sep. 22, 2014
Sales Price					$ 4,451
Book Value and Sales Cost					3,033
Gain/(Loss)					$ 1,418
Units | Unit			83		83
Commercial Industrial [Member] | 198,600 sq ft Eagan 2785 & 2795 - Eagan, MN [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Date Disposed					Jul. 15, 2014
Sales Price					$ 3,600
Book Value and Sales Cost					5,393
Gain/(Loss)					$ (1,793)
Area of real estate property | ft²			198,600		198,600
Other [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sales Price					$ 8,855
Book Value and Sales Cost					10,224
Gain/(Loss)					$ (1,369)
Other [Member] | 117,144 sq ft Thresher Square - Minneapolis, MN [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Date Disposed				May 18, 2015
Sales Price				$ 7,000
Book Value and Sales Cost				7,175
Gain/(Loss)				$ (175)
Area of real estate property | ft²		117,144		117,144
Other [Member] | 2,549,222 sq ft Office Sale Portfolio [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Date Disposed	[1]			Aug. 03, 2015
Sales Price	[1]			$ 250,000
Book Value and Sales Cost	[1]			231,537
Gain/(Loss)	[1]			$ 18,463
Area of real estate property | ft²	[1]	2,549,222		2,549,222
Other [Member] | 420,216 sq ft Mendota Office Center Portfolio - Mendota Heights, MN [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Date Disposed	[2]			Aug. 12, 2015
Sales Price	[2]			$ 40,000
Book Value and Sales Cost	[2]			41,574
Gain/(Loss)	[2]			$ (1,574)
Area of real estate property | ft²	[2]	420,216		420,216
Other [Member] | 1,027,208 sq ft Retail Sale Portfolio [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Date Disposed	[3]			Sep. 30, 2015
Sales Price	[3]			$ 78,960
Book Value and Sales Cost	[3]			71,913
Gain/(Loss)	[3]			$ 7,047
Area of real estate property | ft²	[3]	1,027,208		1,027,208
Other [Member] | 48,700 sq ft Eden Prairie 6101 Blue Circle Drive - Eden Prairie, MN [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Date Disposed				Oct. 19, 2015
Sales Price				$ 2,900
Book Value and Sales Cost				2,928
Gain/(Loss)				$ (28)
Area of real estate property | ft²		48,700		48,700
Other [Member] | 73,338 sq ft Dewey Hill - Edina, MN [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Date Disposed					May 19, 2014
Sales Price					$ 3,100
Book Value and Sales Cost					3,124
Gain/(Loss)					$ (24)
Area of real estate property | ft²			73,338		73,338
Other [Member] | 25,644 sq ft Weston Retail - Weston, WI [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Date Disposed					Jul. 28, 2014
Sales Price					$ 0
Book Value and Sales Cost					1,176
Gain/(Loss)					$ (1,176)
Area of real estate property | ft²			25,644		25,644
Other [Member] | 74,568 sq ft Wirth Corporate Center - Golden Valley, MN [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Date Disposed					Aug. 29, 2014
Sales Price					$ 4,525
Book Value and Sales Cost					4,695
Gain/(Loss)					$ (170)
Area of real estate property | ft²			74,568		74,568
Other [Member] | 52,000 sq ft Kalispell Retail - Kalispell, MT [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Date Disposed					Oct. 15, 2014
Sales Price					$ 1,230
Book Value and Sales Cost					1,229
Gain/(Loss)					$ 1
Area of real estate property | ft²			52,000		52,000

[1] The properties included in this portfolio disposition are: 610 Business Center, 7800 West Brown Deer Road, Ameritrade, Barry Pointe Office Park, Benton Business Park, Brenwood, Brook Valley I, Crosstown Centre, Golden Hills Office Center, Granite Corporate Center, Great Plains, Highlands Ranch I, Highlands Ranch II, Interlachen Corporate Center, Intertech Building, Minnesota National Bank, Northpark Corporate Center, Omaha 10802 Farnam Dr, Plaza VII, Plymouth 5095 Nathan Lane, Prairie Oak Business Center, Rapid City 900 Concourse Drive, Spring Valley IV, Spring Valley V, Spring Valley X, Spring Valley XI, Superior Office Building, TCA Building, Three Paramount Plaza, UHC Office, US Bank Financial Center, Wells Fargo Center, West River Business Park and Westgate.

[2] The properties included in this portfolio disposition are: Mendota Office Center I, Mendota Office Center II, Mendota Office Center III, Mendota Office Center IV and American Corporate Center.

[3] The properties included in this portfolio disposition are: Champlin South Pond, Chan West Village, Duluth 4615 Grand, Duluth Denfeld Retail, Forest Lake Auto, Forest Lake Westlake Center, Grand Forks Medpark Mall, Jamestown Buffalo Mall, Jamestown Business Center, Monticello C Store & vacant land, Omaha Barnes & Noble, Pine City Evergreen Square, Rochester Maplewood Square and St. Cloud Westgate.