Acquisitions and Dispositions - Property Acquisitions (Details)	3 Months Ended	9 Months Ended
	Jun. 30, 2018 USD ($) property property_Unit	Jun. 30, 2018 USD ($) property property_Unit	Jun. 30, 2017 USD ($) property
Real Estate Properties
No. of Units | property_Unit	10,121	10,121
Acquisition Mortgage Debt	$ 164,310,000	$ 164,310,000
Corporate Joint Venture | VIE | Multi-family | Property Acquisition
Real Estate Properties
No. of Units | property	1,921	1,921	1,486
Purchase Price	$ 230,296,000	$ 230,296,000	$ 204,016,000
Initial BRT Equity		49,985,000	47,131,000
Capitalized acquisition costs		$ 3,102,000	$ 2,761,000
Corporate Joint Venture | VIE | Madison, AL | Multi-family | Property Acquisition
Real Estate Properties
No. of Units | property	204	204
Purchase Price	$ 18,420,000	$ 18,420,000
Initial BRT Equity		$ 4,456,000
Ownership Percentage		80.00%
Capitalized acquisition costs		$ 247,000
Corporate Joint Venture | VIE | Boerne, TX | Multi-family | Property Acquisition
Real Estate Properties
No. of Units | property	120	120
Purchase Price	$ 12,000,000	$ 12,000,000
Initial BRT Equity		$ 3,780,000
Ownership Percentage		80.00%
Capitalized acquisition costs		$ 244,000
Corporate Joint Venture | VIE | Boerne, TX | Land | Property Acquisition
Real Estate Properties
Land acquisition		$ 500,000
Corporate Joint Venture | VIE | Ocoee, FL | Multi-family | Property Acquisition
Real Estate Properties
No. of Units | property	522	522
Purchase Price	$ 71,347,000	$ 71,347,000
Initial BRT Equity		$ 12,370,000
Ownership Percentage		50.00%
Capitalized acquisition costs		$ 1,047,000
Corporate Joint Venture | VIE | Lawrenceville, GA | Multi-family | Property Acquisition
Real Estate Properties
No. of Units | property	586	586
Purchase Price	$ 77,229,000	$ 77,229,000
Initial BRT Equity		$ 15,179,000
Ownership Percentage		50.00%
Capitalized acquisition costs		$ 767,000
Corporate Joint Venture | VIE | Daytona, FL | Multi-family | Property Acquisition
Real Estate Properties
No. of Units | property	208	208
Purchase Price	$ 20,500,000	$ 20,500,000
Initial BRT Equity		$ 6,900,000
Ownership Percentage		80.00%
Capitalized acquisition costs		$ 386,000
Corporate Joint Venture | VIE | Grand Prairie, TX | Multi-family | Property Acquisition
Real Estate Properties
No. of Units | property	281	281
Purchase Price	$ 30,800,000	$ 30,800,000
Initial BRT Equity		$ 7,300,000
Ownership Percentage		50.00%
Capitalized acquisition costs		$ 411,000
Corporate Joint Venture | VIE | Pensacola, FL | Multi-family | Property Acquisition
Real Estate Properties
Purchase Price	$ 250,000	250,000
Ownership Percentage	2.50%
Corporate Joint Venture | VIE | Fredricksburg, VA | Multi-family | Property Acquisition
Real Estate Properties
No. of Units | property			220
Purchase Price			$ 38,490,000
Initial BRT Equity			$ 8,720,000
Ownership Percentage			80.00%
Capitalized acquisition costs			$ 643,000
Corporate Joint Venture | VIE | St. Louis, MO | Multi-family | Property Acquisition
Real Estate Properties
No. of Units | property			128
Purchase Price			$ 27,000,000
Initial BRT Equity			$ 6,001,000
Ownership Percentage			75.50%
Capitalized acquisition costs			$ 423,000
Corporate Joint Venture | VIE | St. Louis, MO (Location 2) | Multi-family | Property Acquisition
Real Estate Properties
No. of Units | property			53
Purchase Price			$ 8,000,000
Initial BRT Equity			$ 2,002,000
Ownership Percentage			75.50%
Capitalized acquisition costs			$ 134,000
Corporate Joint Venture | VIE | Creve Coeur, MO | Multi-family | Property Acquisition
Real Estate Properties
No. of Units | property			174
Purchase Price			$ 39,600,000
Initial BRT Equity			$ 9,408,000
Ownership Percentage			78.00%
Capitalized acquisition costs			$ 569,000
Corporate Joint Venture | VIE | West Nashville, TN | Multi-family | Property Acquisition
Real Estate Properties
No. of Units | property			402
Purchase Price			$ 5,228,000
Initial BRT Equity			$ 4,800,000
Ownership Percentage			58.00%
Capitalized acquisition costs			$ 0
Corporate Joint Venture | VIE | Farmers Branch, TX | Multi-family | Property Acquisition
Real Estate Properties
No. of Units | property			509
Purchase Price			$ 85,698,000
Initial BRT Equity			$ 16,200,000
Ownership Percentage			50.00%
Capitalized acquisition costs			$ 992,000
Mortgages payable | Corporate Joint Venture | VIE | Multi-family | Property Acquisition
Real Estate Properties
Acquisition Mortgage Debt	$ 164,310,000	164,310,000	140,340,000
Mortgages payable | Corporate Joint Venture | VIE | Madison, AL | Multi-family | Property Acquisition
Real Estate Properties
Acquisition Mortgage Debt	15,000,000	15,000,000
Mortgages payable | Corporate Joint Venture | VIE | Boerne, TX | Multi-family | Property Acquisition
Real Estate Properties
Acquisition Mortgage Debt	9,200,000	9,200,000
Mortgages payable | Corporate Joint Venture | VIE | Ocoee, FL | Multi-family | Property Acquisition
Real Estate Properties
Acquisition Mortgage Debt	53,060,000	53,060,000
Mortgages payable | Corporate Joint Venture | VIE | Lawrenceville, GA | Multi-family | Property Acquisition
Real Estate Properties
Acquisition Mortgage Debt	54,447,000	54,447,000
Mortgages payable | Corporate Joint Venture | VIE | Daytona, FL | Multi-family | Property Acquisition
Real Estate Properties
Acquisition Mortgage Debt	13,608,000	13,608,000
Mortgages payable | Corporate Joint Venture | VIE | Grand Prairie, TX | Multi-family | Property Acquisition
Real Estate Properties
Acquisition Mortgage Debt	$ 18,995,000	$ 18,995,000
Mortgages payable | Corporate Joint Venture | VIE | Fredricksburg, VA | Multi-family | Property Acquisition
Real Estate Properties
Acquisition Mortgage Debt			29,940,000
Mortgages payable | Corporate Joint Venture | VIE | St. Louis, MO | Multi-family | Property Acquisition
Real Estate Properties
Acquisition Mortgage Debt			20,000,000
Mortgages payable | Corporate Joint Venture | VIE | St. Louis, MO (Location 2) | Multi-family | Property Acquisition
Real Estate Properties
Acquisition Mortgage Debt			6,200,000
Mortgages payable | Corporate Joint Venture | VIE | Creve Coeur, MO | Multi-family | Property Acquisition
Real Estate Properties
Acquisition Mortgage Debt			29,000,000
Mortgages payable | Corporate Joint Venture | VIE | West Nashville, TN | Multi-family | Property Acquisition
Real Estate Properties
Acquisition Mortgage Debt			0
Mortgages payable | Corporate Joint Venture | VIE | Farmers Branch, TX | Multi-family | Property Acquisition
Real Estate Properties
Acquisition Mortgage Debt			$ 55,200,000