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, 2023	Dec. 31, 2022	Dec. 31, 2021
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	$ 334,835	$ 355,212	$ 350,108
Net current-period other comprehensive income (loss)	10,515	(66,865)	(5,799)
Ending balance	372,002	334,835	355,212
Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	(52,771)	14,675	21,447
Other comprehensive income (loss) before classifications	9,747	(67,438)	(6,771)
Amounts reclassified from accumulated other comprehensive income (loss)	0	(8)	(1)
Net current-period other comprehensive income (loss)	9,747	(67,446)	(6,772)
Ending balance	(43,024)	(52,771)	14,675
Defined Benefit Pension Items [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	(5,274)	(5,855)	(6,828)
Other comprehensive income (loss) before classifications	768	581	783
Amounts reclassified from accumulated other comprehensive income (loss)	0	0	190
Net current-period other comprehensive income (loss)	768	581	973
Ending balance	(4,506)	(5,274)	(5,855)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning balance	(58,045)	8,820	14,619
Other comprehensive income (loss) before classifications	10,515	(66,857)	(5,988)
Amounts reclassified from accumulated other comprehensive income (loss)	0	(8)	189
Net current-period other comprehensive income (loss)	10,515	(66,865)	(5,799)
Ending balance	$ (47,530)	$ (58,045)	$ 8,820