Accumulated Other Comprehensive Income - Changes in Each Component of Accumulated Other Comprehensive Income (Loss), Net of Tax (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 352,413	$ 336,613	$ 350,108	$ 330,126
Total other comprehensive income (loss)	(2,395)	733	(5,321)	7,513
Ending balance	348,450	342,055	348,450	342,055
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	18,392	19,549	21,447	12,883
Other comprehensive income (loss) before reclassifications	(2,455)	749	(5,512)	7,415
Amounts reclassified from accumulated other comprehensive income (loss)	(4)	(73)	(2)	(73)
Total other comprehensive income (loss)	(2,459)	676	(5,514)	7,342
Ending balance	15,933	20,225	15,933	20,225
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(6,699)	(5,895)	(6,828)	(6,009)
Amounts reclassified from accumulated other comprehensive income (loss)	64	57	193	171
Total other comprehensive income (loss)	64	57	193	171
Ending balance	(6,635)	(5,838)	(6,635)	(5,838)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	11,693	13,654	14,619	6,874
Other comprehensive income (loss) before reclassifications	(2,455)	749	(5,512)	7,415
Amounts reclassified from accumulated other comprehensive income (loss)	60	(16)	191	98
Total other comprehensive income (loss)	(2,395)	733	(5,321)	7,513
Ending balance	$ 9,298	$ 14,387	$ 9,298	$ 14,387