Accumulated Other Comprehensive Income (Loss) - Schedule of Changes in Accumulated Other Comprehensive Income (Loss) by Component Net of Tax (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized holding gain on available-for-sale securities arising during the period, Pretax	$ (255)	$ 128	$ 1,132	$ 1,455
Reclassify gain included in income, Pretax		(1)		(1)
Unrealized holding gain on available-for-sale securities arising during the period, Tax Effect	(78)	103	414	661
Reclassify gain included in income, Tax effect	0	0	0	0
Beginning balance, After-tax			(874)
Other comprehensive income (loss)	(150)	199	802	1,284
Ending Balance, After-tax	(72)		(72)
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, Pretax	121	1,012	(1,323)	(631)
Unrealized holding gain on available-for-sale securities arising during the period, Pretax	(255)	128	1,132	1,455
Reclassify gain included in income, Pretax		(1)		(1)
Amortization of held-to-maturity discount resulting from transfer, Pretax	27	175	84	491
Total other comprehensive income (loss), Pretax	(228)	302	1,216	1,945
Ending balance, Pretax	(107)	1,314	(107)	1,314
Beginning balance, Tax Effect	(43)	(344)	449	214
Unrealized holding gain on available-for-sale securities arising during the period, Tax Effect	87	(43)	(385)	(494)
Reclassify gain included in income, Tax effect	0	0	0	0
Amortization of held-to-maturity discount resulting from transfer, Tax Effect	(9)	(60)	(29)	(167)
Total other comprehensive income (loss), Tax Effect	78	(103)	(414)	(661)
Ending Balance, Tax Effect	35	(447)	35	(447)
Beginning balance, After-tax	78	668	(874)	(417)
Unrealized holding gain on available-for-sale securities arising during the period, After-tax	(168)	85	747	961
Reclassify gain included in income, After tax		(1)		(1)
Amortization of held-to-maturity discount resulting from transfer, After-tax	18	115	55	324
Other comprehensive income (loss)	(150)	199	802	1,284
Ending Balance, After-tax	$ (72)	$ 867	$ (72)	$ 867