DEBT - Narrative (Details)	9 Months Ended	12 Months Ended
	Jan. 31, 2018	Apr. 30, 2018 USD ($) property loan extension	Apr. 30, 2017 USD ($)
Line of Credit Facility [Line Items]
Number of real estate properties, owned | property		99
Number of real estate properties, serving as collateral for mortgage loans | property		58
Property owned		$ 1,669,764,000	$ 1,358,529,000
Number of real estate properties, unemcumbered by mortgages | property		41
Number of real estate properties, unemcumbered used to provide credit support | property		30
Amount available		$ 6,000,000.0
Revolving line of credit		124,000,000	57,050,000
Carrying principal value		706,140,000	$ 786,030,000
Domestic Line of Credit [Member] | Minimum [Member] | Base Rate [Member]
Line of Credit Facility [Line Items]
Interest rate spread (as a percent)	0.60%
Domestic Line of Credit [Member] | Minimum [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Interest rate spread (as a percent)	1.60%
Domestic Line of Credit [Member] | Maximum [Member] | Base Rate [Member]
Line of Credit Facility [Line Items]
Interest rate spread (as a percent)	1.25%
Domestic Line of Credit [Member] | Maximum [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Interest rate spread (as a percent)	2.25%
Multifamily [Member]
Line of Credit Facility [Line Items]
Property owned		$ 512,100,000
Mortgages [Member]
Line of Credit Facility [Line Items]
Number of loans in default | loan		0
Weighted average interest rate (in hundredths)		4.69%	4.71%
Mortgages [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Interest rate		3.47%
Mortgages [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Interest rate		6.66%
Line of Credit [Member]
Line of Credit Facility [Line Items]
Amount available		$ 300,000,000	$ 250,000,000
Accordion option		$ 200,000,000
Term		1 year
Unsecured Debt [Member]
Line of Credit Facility [Line Items]
Original principal balance		$ 70,000,000
Construction Debt [Member]
Line of Credit Facility [Line Items]
Carrying principal value			$ 41,700,000
Weighted average interest rate (in hundredths)			3.27%
BMO Line of Credit [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Amount available		300,000,000.0	$ 206,000,000
Revolving line of credit		$ 124,000,000	$ 57,100,000
Interest rate (in hundredths)		3.66%
Number of extensions | extension		1
Extension term		12 months
BMO Line of Credit [Member] | Domestic Line of Credit [Member]
Line of Credit Facility [Line Items]
Remaining borrowing capacity		$ 176,000,000