Related-Party Transactions - Former AMA with AAMC Narrative (Details)	Apr. 01, 2015 property extension	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Related Party Transaction [Line Items]
Payable to AAMC | $		$ 34,967,000	$ 5,014,000
AAMC | Affiliated entity
Related Party Transaction [Line Items]
Base management fee, percent of qualified average invested capital	1.50%
Conversion fee, percent of market value of new rental properties	1.50%
Period in fiscal years return on invested equity capital evaluated for termination of agreement	2 years
AAMC | Affiliated entity | Asset management fee, threshold one
Related Party Transaction [Line Items]
Base management fee, percent of qualified average invested capital	25.00%
Incentive management fee, percent of invested capital in excess of threshold	20.00%
AAMC | Affiliated entity | Asset management fee, threshold two
Related Party Transaction [Line Items]
Base management fee, percent of qualified average invested capital	1.75%
Base management fee, number of rental properties floor	2,500
Base management fee, number of rental properties cap	4,499
Incentive management fee, percent of invested capital in excess of threshold	22.50%
Incentive management fee, number of rental properties, floor	2,500
Incentive management fee, number of rental properties cap	4,499
AAMC | Affiliated entity | Asset management fee, threshold three
Related Party Transaction [Line Items]
Base management fee, percent of qualified average invested capital	2.00%
Base management fee, number of rental properties floor	4,500
Incentive management fee, percent of invested capital in excess of threshold	25.00%
Incentive management fee, number of rental properties, floor	4,500
AAMC | Affiliated entity | Management incentive fees
Related Party Transaction [Line Items]
Payable to AAMC | $		$ 0
AAMC | Affiliated entity | Asset Management Agreement
Related Party Transaction [Line Items]
Contract term	15 years
Number of potential renewal extensions | extension	2
Automatic renewal term	5 years
Minimum | AAMC | Affiliated entity
Related Party Transaction [Line Items]
Incentive management fee, return on invested capital	7.00%
Incentive management fee, return on invested capital, per quarter	1.75%
Maximum | AAMC | Affiliated entity
Related Party Transaction [Line Items]
Incentive management fee, return on invested capital	8.25%
Incentive management fee, return on invested capital, per quarter	2.06%