Accumulated Other Comprehensive Income - Amounts Reclassified Out of Each Component of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net gain (loss) on sale of securities	$ (1)		$ (2)
Other operating expenses	(5,781)	$ (2,652)	(8,064)	$ (4,918)
Income tax expense	(1,235)	(825)	(3,275)	(2,001)
Net Income	9,164	6,504	19,922	14,337
Reclassification out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net Income	(65)	(57)	(131)	(114)
Accumulated Other Comprehensive Income (Loss) [Member] | Reclassification out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net Income	(1)		(2)
Accumulated Defined Benefit Plans Adjustment, Actuarial gains/(Losses) [Member] | Reclassification out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other operating expenses	(81)	(72)	(163)	(145)
Income tax expense	17	15	34	31
Net Income	$ (64)	$ (57)	$ (129)	$ (114)