Comprehensive Income - Components of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Tax effect		$ (1,420)
Accumulated other comprehensive loss, net of tax	$ (5,222)	(17,879)
Net unrealized gain (loss) on available for sale securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI before Tax, Attributable to Parent	3,387	(20,974)
Tax effect	(1,001)	6,201
Accumulated other comprehensive loss, net of tax	2,386	(14,773)
Unfunded status of the supplemental retirement plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI before Tax, Attributable to Parent	(11,193)	(4,802)
Tax effect	3,309	1,420
Accumulated other comprehensive loss, net of tax	(7,884)	(3,382)
Joint beneficiary agreement liability, net of tax
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI before Tax, Attributable to Parent	$ 276	$ 276