Other Comprehensive Income - Amounts Reclassified Out of Each Component of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net gain (loss) on sale of securities	$ 3	$ (392)	$ 17	$ (386)
Other operating expenses	(2,719)	(2,498)	(7,944)	(6,358)
Income tax expense	(1,258)	1	(4,688)	(1,407)
Net Income (loss)	7,708	(3,433)	26,038	6,570
Reclassification out of Accumulated Other Comprehensive Loss [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net Income (loss)	(114)	(423)	(335)	(644)
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	(147)	(143)	(441)	(429)
Income tax expense	31	30	93	90
Net Income (loss)	(116)	(113)	(348)	(339)
Unrealized gains 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	3	(392)	17	(386)
Income tax expense	(1)	82	(4)	81
Net Income (loss)	$ 2	$ (310)	$ 13	$ (305)