Other Comprehensive Income (Loss) - Changes in Each Component of Accumulated Other Comprehensive Income (Loss), Net of Tax (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	$ 355,212	$ 350,108	$ 330,126
Net current-period other comprehensive income (loss)	(66,865)	(5,799)	7,745
Ending balance	334,835	355,212	350,108
Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	14,675	21,447	12,883
Other comprehensive income (loss) before classifications	(67,438)	(6,771)	8,638
Amounts reclassified from accumulated other comprehensive income (loss)	(8)	(1)	(74)
Net current-period other comprehensive income (loss)	(67,446)	(6,772)	8,564
Ending balance	(52,771)	14,675	21,447
Defined Benefit Pension Items [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	(5,855)	(6,828)	(6,009)
Other comprehensive income (loss) before classifications	581	783	(1,047)
Amounts reclassified from accumulated other comprehensive income (loss)	0	190	228
Net current-period other comprehensive income (loss)	581	973	(819)
Ending balance	(5,274)	(5,855)	(6,828)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	8,820	14,619	6,874
Other comprehensive income (loss) before classifications	(66,857)	(5,988)	7,591
Amounts reclassified from accumulated other comprehensive income (loss)	(8)	189	154
Net current-period other comprehensive income (loss)	(66,865)	(5,799)	7,745
Ending balance	$ (58,045)	$ 8,820	$ 14,619