COMMITMENTS AND CONTINGENCIES (Details) ft² in Millions	12 Months Ended
	Apr. 30, 2016 USD ($) ft² lease property item	Apr. 30, 2015 USD ($)	Apr. 30, 2014 USD ($)
Real Estate Properties [Line Items]
Number of properties under operating ground and air rights lease | property	9
Rent payable per year under ground lease	$ 329,000
Operating Leases, Future Minimum Payments [Abstract]
2017	330,000
2018	331,000
2019	332,000
2020	333,000
2021	335,000
Thereafter	8,503,000
Total	10,164,000
Tenant improvements	$ 6,100,000
Commitment period for tenant improvements	12 months
Total property cost subject to purchase options	$ 1,681,471,000	$ 1,335,687,000
Total gross rental revenue from properties subject to purchase options	170,698,000	159,969,000	$ 145,028,000
Sale price	$ 536,728,000	88,867,000
Redemption basis	1:1
Minimum redemption holding period	1 year
Number of consecutive trading days for valuation	10 days
Aggregate redemption value of Units of operating partnership owned by limited partners	$ 109,300,000	$ 102,400,000
Minimum [Member]
Real Estate Properties [Line Items]
Lease term of property	15 years
Lease expiration date	Feb. 28, 2031
Number of renewal options | lease	4
Maximum [Member]
Real Estate Properties [Line Items]
Lease term of property	85 years
Lease expiration date	Oct. 31, 2100
Number of renewal options | lease	9
Subject to Purchase Options [Member]
Operating Leases, Future Minimum Payments [Abstract]
Number of properties | property	14
Total property cost subject to purchase options	$ 97,200,000
Total gross rental revenue from properties subject to purchase options	7,600,000
Subject to Purchase Options [Member] | Subsequent Event [Member]
Operating Leases, Future Minimum Payments [Abstract]
Sale price	$ 43,500,000
Subject to Restrictions on Taxable Dispositions [Member]
Operating Leases, Future Minimum Payments [Abstract]
Number of properties | property	76
Real estate investment amount of properties (net of accumulated depreciation)	$ 692,400,000
Combined Commercial Segments [Member] | Subject to Restrictions on Taxable Dispositions [Member]
Operating Leases, Future Minimum Payments [Abstract]
Area of real estate property | ft²	2.6
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	5,396
Discontinued Operations, Held-for-sale [Member]
Operating Leases, Future Minimum Payments [Abstract]
Tenant improvements	$ 101,000