DEBT - Narrative (Details)	8 Months Ended
	Dec. 31, 2018 USD ($) property loan extension	Apr. 30, 2018 USD ($)	Apr. 30, 2017 USD ($)
Line of Credit Facility [Line Items]
Number of apartment communities | property	87
Number of real estate properties, unencumbered by mortgages | property	40
Number of real estate properties, unencumbered used to provide credit support | property	32
Amount available	$ 6,000,000.0
Revolving line of credit	57,500,000	$ 124,000,000	$ 57,050,000
Carrying principal value	648,474,000	706,140,000	$ 786,030,000
Domestic Line of Credit
Line of Credit Facility [Line Items]
Revolving line of credit	$ 0	$ 0
Domestic Line of Credit | Minimum | Base Rate
Line of Credit Facility [Line Items]
Interest rate spread (as a percent)	0.35%
Domestic Line of Credit | Minimum | London Interbank Offered Rate (LIBOR)
Line of Credit Facility [Line Items]
Interest rate spread (as a percent)	1.35%
Domestic Line of Credit | Maximum | Base Rate
Line of Credit Facility [Line Items]
Interest rate spread (as a percent)	8.50%
Domestic Line of Credit | Maximum | London Interbank Offered Rate (LIBOR)
Line of Credit Facility [Line Items]
Interest rate spread (as a percent)	1.90%
Multifamily
Line of Credit Facility [Line Items]
Number of apartment communities, serving as collateral for mortgage loans | property	51
Mortgages
Line of Credit Facility [Line Items]
Number of loans in default | loan	0
Weighted average interest rate (in hundredths)	4.58%	4.69%	4.71%
Mortgages | Minimum
Line of Credit Facility [Line Items]
Interest rate	3.47%
Mortgages | Maximum
Line of Credit Facility [Line Items]
Interest rate	6.66%
Line of Credit
Line of Credit Facility [Line Items]
Term	1 year
Construction Debt
Line of Credit Facility [Line Items]
Carrying principal value			$ 41,700,000
Weighted average interest rate (in hundredths)			3.27%
BMO Line of Credit | Line of Credit
Line of Credit Facility [Line Items]
Amount available	$ 250,000,000.0	$ 300,000,000.0	$ 206,000,000
Revolving line of credit		$ 124,000,000	$ 57,100,000
Number of extensions | extension	1
Extension term	12 months
BMO Line of Credit | Domestic Line of Credit
Line of Credit Facility [Line Items]
Amount available	$ 232,500,000.0
Remaining borrowing capacity	175,000,000
Revolving line of credit	$ 57,500,000
Interest rate (in hundredths)	3.72%
Term Loan Maturing 2024 | Unsecured Debt
Line of Credit Facility [Line Items]
Original principal balance	$ 70,000,000
Term Loan Maturing 2025 | Unsecured Debt
Line of Credit Facility [Line Items]
Original principal balance	$ 75,000,000
Long-term debt, term	7 years