Comprehensive Loss - Components of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net of tax	$ (225,416)	$ (193,905)
Net unrealized loss on available for sale securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, before tax	(335,286)	(290,549)
Accumulated other comprehensive loss, tax effect	99,123	85,897
Accumulated other comprehensive loss, net of tax	(236,163)	(204,652)
Unfunded status of the supplemental retirement plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, before tax	13,901	13,901
Accumulated other comprehensive loss, tax effect	(4,110)	(4,110)
Accumulated other comprehensive loss, net of tax	9,791	9,791
Joint beneficiary agreement liability
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, before tax	956	956
Accumulated other comprehensive loss, tax effect	0	0
Accumulated other comprehensive loss, net of tax	$ 956	$ 956