Changes in Accumulated Other Comprehensive Income (Loss), net - Components of Accumulated Other Comprehensive Income (Loss) Net of Deferred Taxes (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019		Jun. 30, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	$ 119,937	$ 114,919	$ 117,476	[1]	$ 114,554
Change in net unrealized holding gain (loss) on available-for-sale securities	628	(215)	1,434		(1,159)
Balance at end of period	122,617	115,724	122,617		115,724
Net Unrealized Gains (Losses) on Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(446)	(1,433)	(1,252)		(489)
Change in net unrealized holding gain (loss) on available-for-sale securities	628	(215)	1,434		(1,159)
Balance at end of period	182	(1,648)	182		(1,648)
Pension and Post-retirement Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(75)	(667)	(75)		(667)
Balance at end of period	(75)	(667)	(75)		(667)
Accumulated Other Comprehensive Income (Loss), net
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(521)	(2,100)	(1,327)		(1,156)
Change in net unrealized holding gain (loss) on available-for-sale securities	628	(215)	1,434		(1,159)
Balance at end of period	$ 107	$ (2,315)	$ 107		$ (2,315)

[1] Derived from audited December 31, 2018 Consolidated Financial Statements.