Organization and Significant Accounting Policies - Additional Information (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2019 USD ($)
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Description of management fee	In exchange for services provided, our Manager receives a management fee, paid monthly in arrears, in an amount equal to one-twelfth of 1.20% of our Equity (as defined in the Management Agreement).
Annual management fee as a percent of equity	1.20%
Building Estimated Useful Life	27 years 6 months
Building Salvage Value	$ 0
Unrecognized tax benefits	0
Unrecognized tax benefits, accrued interest or penalties	$ 0
Minimum | Agency MBS
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
MBS initial fixed interest rate required, period	1 year
Maximum | Agency MBS
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
MBS initial fixed interest rate required, period	10 years