Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Contingency [Line Items]
Federal (net of state benefit) - enactment of tax reform	$ 1,100,000		$ 1,100,000
Income tax benefit for deferred tax temporary differences		$ 300,000
Amount for which no federal income tax provision has been made	6,000,000	6,000,000	6,000,000	$ 6,000,000
Unrecognized tax benefits	0	0	0
Accrued interest or penalties	$ 0	0	$ 0
State and Local Jurisdiction [Member]
Income Tax Contingency [Line Items]
Operating loss carryforwards		$ 59,800,000
Operating loss carryforwards, expiration year		2019
Minimum [Member]
Income Tax Contingency [Line Items]
Open tax years		2015