Changes in Accumulated Other Comprehensive Income (Loss), net - Components of Accumulated Other Comprehensive Income (Loss), Net of Deferred Income Taxes (Parenthetical) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Change in net unrealized holding gain on available-for-sale securities, deferred income tax expense	$ 13	$ 62	$ 307	$ 443
Net Unrealized Gains (Losses) on Available-for-sale Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Change in net unrealized holding gain on available-for-sale securities, deferred income tax expense	$ 13	$ 62	307	$ 443
Reclassification for previously unrealized net gains (losses) recognized in net income, tax expense			$ 6