Income Taxes - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	May 31, 2013	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2018
Tax Credit Carryforward [Line Items]
Annual distribution of net taxable income for U.S. federal income tax not to apply to our earnings that we distribute (percent)				90.00%
Net taxable income subject to distribution (percent)				100.00%
Excise tax rate				4.00%
Income tax provision (benefit)		$ (721,000)	$ 48,000	$ (573,000)	$ 272,000
Tax credit refund		747,000		$ 747,000
U.S. federal corporate income tax rate				21.00%		35.00%
Common stock, shares issued	25,875,000			10,535,507	11,484,414
Net operating losses carried forward							$ 159,000,000.0
NOLs expiration date				Dec. 31, 2029
Open tax year	2015 2017 2018
Internal Revenue Service [Member]
Tax Credit Carryforward [Line Items]
Net operating losses limit per annum		$ 2,000,000.0		$ 2,000,000.0
Net operating losses limitations				the availability of our NOLs is generally limited to $2.0 million per annum