ACQUISITIONS, DEVELOPMENT PROJECTS PLACED IN SERVICE AND DISPOSITIONS, PROPERTY DISPOSITIONS (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Oct. 31, 2016 ft² property	Oct. 31, 2015 ft² property	Oct. 31, 2016 USD ($) ft²	Oct. 31, 2015 USD ($) ft²
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sale price			$ 57,550	$ 378,860
Book value and sales cost			42,089	355,127
Gain/(Loss)			$ 15,461	$ 23,733
Healthcare [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties sold | property	8	1
Healthcare [Member] | Idaho Spring Creek Senior Housing Properties [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Date disposed			Oct. 31, 2016
Sale price			$ 43,900
Book value and sales cost			37,397
Gain/(Loss)			$ 6,503
Area of real estate property | ft²	189,244		189,244
Other [Member] | Stone Container - Fargo, ND [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Date disposed			Jul. 25, 2016
Sale price			$ 13,400
Book value and sales cost			4,418
Gain/(Loss)			$ 8,982
Area of real estate property | ft²	195,075		195,075
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
Sale 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				Aug. 03, 2015
Sale price				$ 250,000
Book value and sales cost				231,537
Gain/(Loss)				$ 18,463
Area of real estate property | ft²		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				Aug. 12, 2015
Sale price				$ 40,000
Book value and sales cost				41,574
Gain/(Loss)				$ (1,574)
Area of real estate property | ft²		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				Sep. 30, 2015
Sale price				$ 78,960
Book value and sales cost				71,913
Gain/(Loss)				$ 7,047
Area of real estate property | ft²		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
Sale price				$ 2,900
Book value and sales cost				2,928
Gain/(Loss)				$ (28)
Area of real estate property | ft²		48,700		48,700
Office [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties sold | property		39
Retail [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties sold | property		15
Unimproved Land [Member] | Georgetown Square - Grand Chute, WI [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Date disposed			May 06, 2016
Sale price			$ 250
Book value and sales cost			274
Gain/(Loss)			$ (24)