ACQUISITIONS, DISPOSITIONS AND IMPAIRMENT CHARGES - Schedule of Property Dispositions (Details)	12 Months Ended
	Sep. 30, 2018 USD ($) property_unit	Sep. 30, 2017 USD ($) property_unit	Sep. 30, 2016 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
No. of Units | property_unit	10,121
Gain on Sale	$ 0	$ 0	$ (2,788,000)
Impairment of real estate	$ 0	$ 0	$ 0
Disposition of real estate properties
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
No. of Units | property_unit	1,370	1,581
Sales Price	$ 171,420,000	$ 169,760,000
Gain on Sale	64,925,000	52,601,000
Non-controlling partner portion of gain	$ 27,644,000	$ 24,840,000
Disposition of real estate properties | Melbourne, FL
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
No. of Units | property_unit	208
Sales Price	$ 22,250,000
Gain on Sale	12,519,000
Non-controlling partner portion of gain	$ 2,504,000
Disposition of real estate properties | New York, NY (Location 1)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
No. of Units | property_unit	1	1
Sales Price	$ 470,000	$ 465,000
Gain on Sale	439,000	449,000
Non-controlling partner portion of gain	$ 0	$ 0
Disposition of real estate properties | Valley, AL
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
No. of Units | property_unit	618
Sales Price	$ 51,000,000
Gain on Sale	9,712,000
Non-controlling partner portion of gain	$ 4,547,000
Disposition of real estate properties | Palm Beach Gardens, FL
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
No. of Units | property_unit	542
Sales Price	$ 97,250,000
Gain on Sale	41,831,000
Non-controlling partner portion of gain	$ 20,593,000
Disposition of real estate properties | New York, NY (Location 2)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
No. of Units | property_unit	1
Sales Price	$ 450,000
Gain on Sale	424,000
Non-controlling partner portion of gain	$ 0
Disposition of real estate properties | Greenville, NC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
No. of Units | property_unit		350
Sales Price		$ 68,000,000
Gain on Sale		18,483,000
Non-controlling partner portion of gain		$ 9,329,000
Disposition of real estate properties | Panama City, FL
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
No. of Units | property_unit		160
Sales Price		$ 14,720,000
Gain on Sale		7,393,000
Non-controlling partner portion of gain		$ 3,478,000
Disposition of real estate properties | Atlanta, GA
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
No. of Units | property_unit		350
Sales Price		$ 36,750,000
Gain on Sale		8,905,000
Non-controlling partner portion of gain		$ 4,166,000
Disposition of real estate properties | Hixson, TN
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
No. of Units | property_unit		156
Sales Price		$ 10,775,000
Gain on Sale		608,000
Non-controlling partner portion of gain		$ 152,000
Disposition of real estate properties | Humble, TX (Parkside)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
No. of Units | property_unit		260
Sales Price		$ 18,000,000
Gain on Sale		7,707,000
Non-controlling partner portion of gain		$ 3,143,000
Disposition of real estate properties | Humble, TX (Meadowbrook)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
No. of Units | property_unit		160
Sales Price		$ 11,300,000
Gain on Sale		4,767,000
Non-controlling partner portion of gain		$ 1,943,000
Disposition of real estate properties | Pasadena, TX
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
No. of Units | property_unit		144
Sales Price		$ 9,750,000
Gain on Sale		4,289,000
Non-controlling partner portion of gain		$ 2,629,000