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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net gain (loss) on sale of securities		$ 10		$ 14
Other operating expenses	$ (2,652)	(2,391)	$ (4,918)	(4,519)
Income tax expense	(825)	(1,546)	(2,001)	(3,430)
Net Income	6,504	8,661	14,337	18,330
Reclassification out of Accumulated Other Comprehensive Loss [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net Income	(57)	(108)	(114)	(221)
Unrealized Gains (Losses) on Available-for-Sale Securities [Member] | Reclassification out of Accumulated Other Comprehensive Loss [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net gain (loss) on sale of securities		10		14
Income tax expense		(2)		(3)
Net Income		8		11
Accumulated Defined Benefit Plans Adjustment, Actuarial gains/(Losses) [Member] | Reclassification out of Accumulated Other Comprehensive Loss [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other operating expenses	(72)	(147)	(145)	(294)
Income tax expense	15	31	31	62
Net Income	$ (57)	$ (116)	$ (114)	$ (232)