Comprehensive Income (Loss) - Components of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income, net of tax	$ 8,167	$ 12,280
Net unrealized gain on available for sale securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income, before tax	14,238	19,183
Accumulated other comprehensive income, tax effect	(4,210)	(5,671)
Accumulated other comprehensive income, net of tax	10,028	13,512
Unfunded status of the supplemental retirement plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income, before tax	(1,294)	(1,294)
Accumulated other comprehensive income, tax effect	382	382
Accumulated other comprehensive income, net of tax	(912)	(912)
Joint beneficiary agreement liability
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income, before tax	(949)	(320)
Accumulated other comprehensive income, tax effect	0	0
Accumulated other comprehensive income, net of tax	$ (949)	$ (320)