Nature of Business and Operations - Initial Offering Price (Details) - $ / shares	Sep. 30, 2020	Mar. 19, 2020	Mar. 21, 2019	Jun. 27, 2018
Class of Stock [Line Items]
Net asset value		$ 9.01	$ 9.12	$ 9.05
Class A
Class of Stock [Line Items]
Net asset value			9.12
Class A \| Primary Offering Price \| Inception through July 2, 2017
Class of Stock [Line Items]
Primary Offering Price	$ 10.00
Class A \| Shares issued through distribution reinvestment plan \| Inception through July 2, 2017
Class of Stock [Line Items]
Primary Offering Price	9.60
Class A \| Shares issued through distribution reinvestment plan \| July 3, 2017 through July 1, 2018
Class of Stock [Line Items]
Primary Offering Price	9.60
Class A \| Shares issued through distribution reinvestment plan \| July 2, 2018 through March 24, 2019
Class of Stock [Line Items]
Primary Offering Price	9.05
Class A \| Shares issued through distribution reinvestment plan \| March 25, 2019 through March 20, 2020
Class of Stock [Line Items]
Primary Offering Price	9.12
Class A \| Shares issued through distribution reinvestment plan \| March 21, 2020 through September 30, 2020
Class of Stock [Line Items]
Primary Offering Price	9.01
Class T Common Stock
Class of Stock [Line Items]
Net asset value			9.12
Class T Common Stock \| Primary Offering Price \| Inception through July 2, 2017
Class of Stock [Line Items]
Primary Offering Price	9.47
Class T Common Stock \| Shares issued through distribution reinvestment plan \| Inception through July 2, 2017
Class of Stock [Line Items]
Primary Offering Price	9.09
Class T Common Stock \| Shares issued through distribution reinvestment plan \| July 3, 2017 through July 1, 2018
Class of Stock [Line Items]
Primary Offering Price	9.09
Class T Common Stock \| Shares issued through distribution reinvestment plan \| July 2, 2018 through March 24, 2019
Class of Stock [Line Items]
Primary Offering Price	9.05
Class T Common Stock \| Shares issued through distribution reinvestment plan \| March 25, 2019 through March 20, 2020
Class of Stock [Line Items]
Primary Offering Price	9.12
Class T Common Stock \| Shares issued through distribution reinvestment plan \| March 21, 2020 through September 30, 2020
Class of Stock [Line Items]
Primary Offering Price	9.01
Class R Common Stock
Class of Stock [Line Items]
Net asset value			9.12
Class R Common Stock \| Primary Offering Price \| July 3, 2017 through July 1, 2018
Class of Stock [Line Items]
Primary Offering Price	9.52
Class R Common Stock \| Primary Offering Price \| July 2, 2018 through March 24, 2019
Class of Stock [Line Items]
Primary Offering Price	9.68
Class R Common Stock \| Primary Offering Price \| March 25, 2019 through October 31, 2019
Class of Stock [Line Items]
Primary Offering Price	9.75
Class R Common Stock \| Shares issued through distribution reinvestment plan \| July 3, 2017 through July 1, 2018
Class of Stock [Line Items]
Primary Offering Price	9.14
Class R Common Stock \| Shares issued through distribution reinvestment plan \| July 2, 2018 through March 24, 2019
Class of Stock [Line Items]
Primary Offering Price	9.05
Class R Common Stock \| Shares issued through distribution reinvestment plan \| March 25, 2019 through March 20, 2020
Class of Stock [Line Items]
Primary Offering Price	9.12
Class I Common Stock
Class of Stock [Line Items]
Net asset value			$ 9.12
Class I Common Stock \| Primary Offering Price \| July 3, 2017 through July 1, 2018
Class of Stock [Line Items]
Primary Offering Price	9.13
Class I Common Stock \| Primary Offering Price \| July 2, 2018 through March 24, 2019
Class of Stock [Line Items]
Primary Offering Price	9.28
Class I Common Stock \| Primary Offering Price \| March 25, 2019 through October 31, 2019
Class of Stock [Line Items]
Primary Offering Price	9.35
Class I Common Stock \| Shares issued through distribution reinvestment plan \| July 3, 2017 through July 1, 2018
Class of Stock [Line Items]
Primary Offering Price	8.90
Class I Common Stock \| Shares issued through distribution reinvestment plan \| July 2, 2018 through March 24, 2019
Class of Stock [Line Items]
Primary Offering Price	9.05
Class I Common Stock \| Shares issued through distribution reinvestment plan \| March 25, 2019 through March 20, 2020
Class of Stock [Line Items]
Primary Offering Price	9.12
Class I Common Stock \| Shares issued through distribution reinvestment plan \| March 21, 2020 through September 30, 2020
Class of Stock [Line Items]
Primary Offering Price	$ 9.01

Resource Apartment REIT III, Inc. 10-Q