Accumulated Other Comprehensive Income (loss) - Schedule of Changes in Accumulated Other Comprehensive (Loss) Income by Component Net of Tax (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized holding gain (loss) on available-for-sale securities arising during the period, Pretax	$ (156)	$ 916	$ (1,467)	$ 1,386
Unrealized holding gain (loss) on available-for-sale securities arising during the period, Tax Effect	(29)	321	(300)	492
Beginning balance, After-tax			(663)
Other comprehensive (loss) income	(107)	621	(1,126)	952
Ending Balance, After-tax	(1,818)		(1,818)
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, Pretax	(2,165)	(821)	(839)	(1,323)
Unrealized holding gain (loss) on available-for-sale securities arising during the period, Pretax	(156)	916	(1,539)	1,386
Reclassify equity AOCI gain to retained earnings, Pretax			36
Amortization of held-to-maturity discount resulting from transfer, Pretax	20	26	41	58
Total other comprehensive income, Pretax	(136)	942	(1,462)	1,444
Ending balance, Pretax	(2,301)	121	(2,301)	121
Beginning balance, Tax Effect	454	278	176	449
Unrealized holding gain (loss) on available-for-sale securities arising during the period, Tax Effect	33	(312)	323	(471)
Reclassify equity AOCI gain to retained earnings, Tax Effect			(7)
Amortization of held-to-maturity discount resulting from transfer, Tax Effect	(4)	(9)	(9)	(21)
Total other comprehensive income, Tax Effect	29	(321)	307	(492)
Ending Balance, Tax Effect	483	(43)	483	(43)
Beginning balance, After-tax	(1,711)	(543)	(663)	(874)
Unrealized holding gain (loss) on available-for-sale securities arising during the period, After-tax	(123)	604	(1,216)	915
Reclassify equity AOCI gain to retained earnings, After-tax			29
Amortization of held-to-maturity discount resulting from transfer, After-tax	16	17	32	37
Other comprehensive (loss) income	(107)	621	(1,155)	952
Ending Balance, After-tax	$ (1,818)	$ 78	$ (1,818)	$ 78