Changes in Accumulated Other Comprehensive Income (Loss), net - Components of Accumulated Other Comprehensive Income (Loss), Net of Deferred Income Taxes (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020		Sep. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	$ 119,690	$ 122,617	$ 126,185	[1]	$ 117,476
Balance at end of period	121,429	124,857	121,429		124,857
Net Unrealized Gains (Losses) on Available-for-sale Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	1,520	182	437		(1,252)
Change in net unrealized holding gain on available-for-sale securities, net of deferred income tax expense	50	233	1,156		1,667
Reclassification for previously unrealized net gains recognized in net income, net of income tax expense of $6			(23)
Balance at end of period	1,570	415	1,570		415
Pension and Post-retirement Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(354)	(75)	(354)		(75)
Balance at end of period	(354)	(75)	(354)		(75)
Accumulated Other Comprehensive Income (Loss ), net
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	1,166	107	83		(1,327)
Change in net unrealized holding gain on available-for-sale securities, net of deferred income tax expense	50	233	1,156		1,667
Reclassification for previously unrealized net gains recognized in net income, net of income tax expense of $6			(23)
Balance at end of period	$ 1,216	$ 340	$ 1,216		$ 340

[1] Derived from audited December 31, 2019 Consolidated Financial Statements.