Comprehensive Income (Loss) - Components of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income, net of tax	$ (169,461)	$ (193,905)
Net unrealized gain on available for sale securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income, before tax	(255,845)	(290,549)
Accumulated other comprehensive income, tax effect	75,637	85,897
Accumulated other comprehensive income, net of tax	(180,208)	(204,652)
Unfunded status of the supplemental retirement plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income, before tax	13,901	13,901
Accumulated other comprehensive income, tax effect	(4,110)	(4,110)
Accumulated other comprehensive income, net of tax	9,791	9,791
Joint beneficiary agreement liability
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income, before tax	956	956
Accumulated other comprehensive income, tax effect	0	0
Accumulated other comprehensive income, net of tax	$ 956	$ 956