Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2018
Tax Credit Carryforward [Line Items]
Unrecognized tax benefits	$ 0	$ 0	$ 0	$ 0
Interest or penalties related to uncertain tax positions	0	0	0	0
Prepaid taxes	100,000		100,000			$ 100,000
Deferred tax assets	2,500,000		2,500,000			2,100,000
Deferred tax liability	2,400,000		$ 2,400,000			$ 1,600,000
Corporate income tax rate			21.00%		35.00%
Tax Year 2015 [Member]
Tax Credit Carryforward [Line Items]
Tax years open to examination			2015
Tax Year 2018 [Member]
Tax Credit Carryforward [Line Items]
Tax years open to examination			2018
General and Administrative Expense [Member]
Tax Credit Carryforward [Line Items]
Federal and state income tax expense (benefit)	$ 500,000	$ 800,000	$ 1,700,000	$ 1,900,000