Income Taxes - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	May 31, 2013	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
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		$ 48,000	$ 83,000	$ 272,000	$ 265,000
Deferred tax assets		0		0		$ 0
Deferred tax liabilities		0		$ 0		$ 0
U.S. federal corporate income tax rate				21.00%		35.00%
Common stock, shares issued	25,875,000			11,484,414	971
Net operating losses carried forward						$ 159,000,000
NOLs expiration date						Dec. 31, 2029
Open tax year				2015 2016 2017
Internal Revenue Service [Member]
Tax Credit Carryforward [Line Items]
Net operating losses limit per annum		$ 2,000,000		$ 2,000,000
Net operating losses limitations				The availability of our NOLs is generally limited to $2.0 million per annum