Accumulated Other Comprehensive Income - Changes in Each Component of Accumulated Other Comprehensive Income (Loss), Net of Tax (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 350,058	$ 328,167	$ 350,108	$ 330,126
Total other comprehensive income (loss)	2,124	3,766	(2,926)	6,780
Ending balance	352,413	336,613	352,413	336,613
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	16,332	15,840	21,447	12,883
Other comprehensive income before reclassifications	2,059	3,709	(3,057)	6,666
Amounts reclassified from accumulated other comprehensive income	1		2
Total other comprehensive income (loss)	2,060	3,709	(3,055)	6,666
Ending balance	18,392	19,549	18,392	19,549
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(6,763)	(5,952)	(6,828)	(6,009)
Amounts reclassified from accumulated other comprehensive income	64	57	129	114
Total other comprehensive income (loss)	64	57	129	114
Ending balance	(6,699)	(5,895)	(6,699)	(5,895)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	9,569	9,888	14,619	6,874
Other comprehensive income before reclassifications	2,059	3,709	(3,057)	6,666
Amounts reclassified from accumulated other comprehensive income	65	57	131	114
Total other comprehensive income (loss)	2,124	3,766	(2,926)	6,780
Ending balance	$ 11,693	$ 13,654	$ 11,693	$ 13,654