Comprehensive Income - Components of Other Comprehensive Income (Loss) and Related Tax Effects (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized holding (losses) gains on available for sale securities before reclassifications	$ (17,057)	$ 6,422	$ (11,015)
Amounts reclassified out of accumulated other comprehensive income:
Realized gains on debt securities	(207)	(961)
Total amounts reclassified out of accumulated other comprehensive income	(570)	(961)
Unrealized holding (losses) gains on available for sale securities after reclassifications	(17,627)	5,461	(11,015)
Tax effect	5,193	(2,296)	4,631
Unrealized holding (losses) gains on available for sale securities, net of tax	(12,434)	3,165	(6,384)
Change in unfunded status of the supplemental retirement plans before reclassifications	762	(1,016)	511
Amounts reclassified out of accumulated other comprehensive income:
Amortization of prior service cost	(54)	(12)	(40)
Amortization of actuarial losses	510	390	550
Total amounts reclassified out of accumulated other comprehensive income	(212)	378	510
Change in unfunded status of the supplemental retirement plans after reclassifications	550	(638)	1,021
Tax effect	(162)	268	(429)
Change in unfunded status of the supplemental retirement plans, net of tax	388	(370)	592
Change in joint beneficiary agreement liability before reclassifications	426	(110)	(343)
Tax effect	0	0	0
Change in unfunded status of the supplemental retirement plans, net of tax	426	(110)	(343)
Other comprehensive (loss) income	(11,620)	$ 2,685	$ (6,135)
ASU 2016-01 [Member]
Amounts reclassified out of accumulated other comprehensive income:
Total amounts reclassified out of accumulated other comprehensive income	62
ASU 2018-02 [Member]
Amounts reclassified out of accumulated other comprehensive income:
Total amounts reclassified out of accumulated other comprehensive income	(425)
Amounts reclassified out of accumulated other comprehensive income:
Total amounts reclassified out of accumulated other comprehensive income	$ (668)

Other comprehensive income loss changes in joint beneficiary agreement liability tax.

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