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, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, net of tax	$ (118)	$ (281)	$ (231)	$ (343)
Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassifications, net of tax	(5)		(5)
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 securities available for sale	(6)		(6)
Income taxes	1		1
Net of tax	5		5
Accumulated Defined Benefit Plans Adjustment, Actuarial Losses [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other operating expenses and Salaries, wages and benefits	(143)	(426)	(286)	(520)
Defined Benefit Pension Items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income taxes	30	145	60	177
Reclassifications, net of tax	$ (113)	$ (281)	$ (226)	$ (343)

Amount before tax, after reclassification adjustments, of appreciation (loss) in value of unsold available-for-sale securities. Excludes amounts related to other than temporary impairment (OTTI) loss.

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Amount of tax expense (benefit), after reclassification adjustments, of appreciation (loss) in value of unsold available-for-sale securities. Excludes amounts related to other than temporary impairment (OTTI) loss.

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