Other Comprehensive Income - Components of Other Comprehensive Income 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]
Total other comprehensive (loss) income	$ (3,653)	$ 15	$ (2,020)
Available for sale securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before reclassifications	(5,073)	(136)	(1,838)
Reclassifications	0	(160)	(83)
Net unrealized gain (loss)	(5,073)	(296)	(1,921)
Tax effect	1,066	104	672
Total other comprehensive (loss) income	(4,007)	(192)	(1,249)
Available for sale securities, portion of OTTI recognized in earnings
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before reclassifications	0	134	(442)
Reclassifications	0	(1,383)	(922)
Net unrealized gain (loss)	0	(1,249)	(1,364)
Tax effect	0	437	477
Total other comprehensive (loss) income	0	(812)	(887)
Unrealized gain (loss) on postretirement benefits plan
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before reclassifications	404	808	(282)
Reclassifications	84	192	184
Net unrealized gain (loss)	488	1,000	(98)
Tax effect	(102)	(175)	34
Total other comprehensive (loss) income	386	825	(64)
Unrealized loss on interest rate swap
Accumulated Other Comprehensive Income (Loss) [Line Items]
Before reclassifications	(204)	10	(63)
Reclassifications	164	288	340
Net unrealized gain (loss)	(40)	298	277
Tax effect	8	(104)	(97)
Total other comprehensive (loss) income	$ (32)	$ 194	$ 180