Comprehensive Income (Loss) - Components of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income, net of tax	$ (164,367)	$ (153,169)
Net unrealized loss on available for sale securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income, before tax	(247,720)	(231,821)
Accumulated other comprehensive income, tax effect	73,235	68,534
Accumulated other comprehensive income, net of tax	(174,485)	(163,287)
Unfunded status of the supplemental retirement plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income, before tax	13,527	13,527
Accumulated other comprehensive income, tax effect	(3,999)	(3,999)
Accumulated other comprehensive income, net of tax	9,528	9,528
Joint beneficiary agreement liability
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income, before tax	590	590
Accumulated other comprehensive income, tax effect	0	0
Accumulated other comprehensive income, net of tax	$ 590	$ 590