Related Party Arrangements - Property Management Fees and Expenses and Other Fees (Details)	6 Months Ended
	Jun. 30, 2019
Property Management Fees and Expenses [Member] \| Steadfast Management Company [Member] \| Property Manager [Member]
Related Party Transaction [Line Items]
Property management fee, percent fee	1.00%
Property Management Fees and Expenses [Member] \| Steadfast Management Company [Member] \| Minimum [Member] \| Property Manager [Member]
Related Party Transaction [Line Items]
Property management fee, percent fee	2.75%
Property Management Fees and Expenses [Member] \| Steadfast Management Company [Member] \| Maximum [Member] \| Property Manager [Member]
Related Party Transaction [Line Items]
Property management fee, percent fee	3.00%
Property Management Agreement, Incentive Management Fee [Member] \| Steadfast Management Company [Member] \| Property Manager [Member]
Related Party Transaction [Line Items]
Property management fee, percent fee	1.00%
Property management agreement, initial term	1 year
Property management agreement, notice of termination option	60 days
Property management agreement, notice of termination breach	30 days
Construction Management Agreement [Member] \| Pacific Coast Land & Construction, Inc. [Member] \| Affiliated Entity [Member]
Related Party Transaction [Line Items]
Construction management fee percentage	6.00%

Steadfast Apartment REIT III, Inc. 10-Q