Summary of Significant Accounting Policies - Subsidiaries (Details)	Sep. 30, 2020 unit
Adair off Addison
Property, Plant and Equipment [Line Items]
Number of Units	152
Uptown Buckhead
Property, Plant and Equipment [Line Items]
Number of Units	216
Crosstown at Chapel Hill
Property, Plant and Equipment [Line Items]
Number of Units	411
The Brookwood
Property, Plant and Equipment [Line Items]
Number of Units	274
Adair off Addison Apartment Homes
Property, Plant and Equipment [Line Items]
Number of Units	200
Montclair Terrace
Property, Plant and Equipment [Line Items]
Number of Units	188
Grand Reserve
Property, Plant and Equipment [Line Items]
Number of Units	319
Verdant Apartment Homes
Property, Plant and Equipment [Line Items]
Number of Units	216
1000 Spalding Apartment Homes
Property, Plant and Equipment [Line Items]
Number of Units	252
Arcadia Apartment Homes
Property, Plant and Equipment [Line Items]
Number of Units	300
Ravina Apartment Homes
Property, Plant and Equipment [Line Items]
Number of Units	498
81 Fifty at West Hills Apartment Homes
Property, Plant and Equipment [Line Items]
Number of Units	357
The Palmer at Las Colinas
Property, Plant and Equipment [Line Items]
Number of Units	476
Windbrooke Crossing
Property, Plant and Equipment [Line Items]
Number of Units	236
The Woods of Burnsville
Property, Plant and Equipment [Line Items]
Number of Units	400
Indigo Creek
Property, Plant and Equipment [Line Items]
Number of Units	408
Martin's Point
Property, Plant and Equipment [Line Items]
Number of Units	256