ACQUISITIONS, DEVELOPMENT PROJECTS PLACED IN SERVICE AND DISPOSITIONS - PROPERTY DISPOSITIONS (Details) - Disposed of by Sale [Member] $ in Thousands	3 Months Ended
	Jul. 31, 2017 USD ($) ft² property	Jul. 31, 2016 USD ($) ft² property
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sale price	$ 3,440	$ 13,650
Book value and sales cost	3,332	4,692
Gain/(Loss)	$ 108	$ 8,958
Retail [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties sold | property	1	1
Other [Member] | Minot Southgate Retail - Minot, ND [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Date disposed	May 15, 2017
Sale price	$ 3,440
Book value and sales cost	3,332
Gain/(Loss)	$ 108
Area of real estate property | ft²	4,998
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
Unimproved Land [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties sold | property		1
Unimproved Land [Member] | Grand Chute, Wisconsin, Unimproved Land [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)