ACQUISITIONS, DEVELOPMENT PROJECTS PLACED IN SERVICE AND DISPOSITIONS - ACQUISITIONS (Details) - Acquisitions Member $ in Thousands	6 Months Ended
Oct. 31, 2017 USD ($) ft² item	Oct. 31, 2016 USD ($)
Acquisitions and development projects placed in service [Abstract]
Total acquisition costs	$ 153,750	$ 0
Form of consideration, cash	153,750
Investment allocation, land	16,418
Investment allocation, building	135,621
Investment allocation, intangible assets	$ 1,711
Multi-Family Residential [Member] \| 191 unit - Oxbo - St. Paul, MN [Member]
Acquisitions and development projects placed in service [Abstract]
Date acquired	May 26, 2017
Total acquisition costs	$ 61,500
Form of consideration, cash	61,500
Investment allocation, land	5,809
Investment allocation, building	54,910
Investment allocation, intangible assets	$ 781
Number of apartment units \| item	191
Area of real estate property \| ft²	11,477
Multi-Family Residential [Member] \| 500 unit - Park Place - Plymouth, MN [Member]
Acquisitions and development projects placed in service [Abstract]
Date acquired	Sep. 13, 2017
Total acquisition costs	$ 92,250
Form of consideration, cash	92,250
Investment allocation, land	10,609
Investment allocation, building	80,711
Investment allocation, intangible assets	$ 930
Number of apartment units \| item	500

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Area of a real estate property.

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Date when the business acquisition agreement was executed, in CCYY-MM-DD format.

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Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 30
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=6911251&loc=d3e6578-128477

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Amount of facility held for productive use including, but not limited to, office, production, storage and distribution facilities, acquired at the acquisition date.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Amount of intangible assets, excluding goodwill, acquired at the acquisition date.

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Amount of real estate acquired, at the acquisition date.

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- Definition

The number of units in a real estate property owned as of the balance sheet date.

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The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Investing Activities
-URI http://asc.fasb.org/extlink&oid=6516133

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-Publisher FASB
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