COMMITMENTS AND CONTINGENCIES (Details) ft² in Millions	12 Months Ended
	Apr. 30, 2017 USD ($) ft² lease property item	Apr. 30, 2016 USD ($)	Apr. 30, 2015 USD ($)
Real Estate Properties [Line Items]
Number of properties under operating ground and air rights lease | property	7
Rent payable per year under ground lease	$ 330,000
Operating Leases, Future Minimum Payments [Abstract]
2018	331,000
2019	332,000
2020	333,000
2021	335,000
2022	336,000
Thereafter	8,167,000
Total	9,834,000
Tenant improvements	$ 4,300,000
Commitment period for tenant improvements	12 months
Total property cost subject to purchase options	$ 1,677,481,000	$ 1,681,471,000
Total gross rental revenue from properties subject to purchase options	$ 186,837,000	170,698,000	$ 159,969,000
Redemption basis	1:1
Number of consecutive trading days for valuation	10 days
Aggregate redemption value of Units of operating partnership owned by limited partners	$ 95,100,000	$ 109,300,000
Minimum [Member]
Real Estate Properties [Line Items]
Lease term of property	14 years
Lease expiration date	Feb. 28, 2031
Number of renewal options | lease	3
Maximum [Member]
Real Estate Properties [Line Items]
Lease term of property	39 years
Lease expiration date	Oct. 31, 2055
Number of renewal options | lease	7
Subject to Purchase Options [Member]
Operating Leases, Future Minimum Payments [Abstract]
Number of properties | property	2
Total property cost subject to purchase options	$ 27,300,000
Total gross rental revenue from properties subject to purchase options	$ 2,700,000
Subject to Restrictions on Taxable Dispositions [Member]
Operating Leases, Future Minimum Payments [Abstract]
Number of properties | property	30
Real estate investment amount of properties (net of accumulated depreciation)	$ 286,700,000
Combined Commercial Segments [Member] | Subject to Restrictions on Taxable Dispositions [Member]
Operating Leases, Future Minimum Payments [Abstract]
Area of real estate property | ft²	431,000.0
Multi-Family Residential [Member] | Subject to Restrictions on Taxable Dispositions [Member]
Operating Leases, Future Minimum Payments [Abstract]
Number of apartment units subject to restrictions on taxable dispositions | item	3,285
Discontinued Operations, Held-for-sale [Member] | Senior Housing properties [Member] | Subject to Purchase Options [Member]
Operating Leases, Future Minimum Payments [Abstract]
Number of real estate properties sold | property	2
Sale price	$ 36,900,000
Discontinued Operations, Held-for-sale [Member] | Unimproved Land [Member] | Subject to Purchase Options [Member]
Operating Leases, Future Minimum Payments [Abstract]
Sale price	$ 3,600,000