Provision for Income Taxes - Provision for Income Taxes (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Expected tax expense, at the U.S. federal statutory income tax rate of 21%	$ 513	$ 1,074	$ 2,270	$ 3,505
State income taxes	90	185	384	588
FDII benefit	(7)	(22)	(39)	(170)	$ (98)
Other, net	14	(10)	25
Total income tax expense	$ 610	$ 1,227	$ 2,640	$ 3,923