Allowance for Loan Losses - Summary of Activity in Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended	12 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Loans and Leases Receivable Disclosure [Line Items]
Beginning Balance	$ 32,064	$ 29,973	$ 32,582	$ 30,323	$ 30,323
Charge-offs	(293)	(318)	(1,019)	(798)	(2,364)
Recoveries	560	507	2,368	873	2,040
Provision (benefit)	537	(638)	(1,063)	(874)	2,583
Ending Balance	32,868	29,524	32,868	29,524	32,582
Mortgage Loans on Real Estate [Member]
Loans and Leases Receivable Disclosure [Line Items]
Beginning Balance	14,830	13,665	15,620	13,758	13,758
Charge-offs	(2)	(66)	(2)	(67)	(92)
Recoveries	13	21	1,396	36	68
Provision (benefit)	(166)	(22)	(2,339)	(129)	1,886
Ending Balance	14,675	13,598	14,675	13,598	15,620
Mortgage Loans on Real Estate [Member] \| Commercial [Member]
Loans and Leases Receivable Disclosure [Line Items]
Beginning Balance	12,330	11,495	12,944	11,441	11,441
Charge-offs		(15)		(15)	(15)
Recoveries	10	21	1,391	36	68
Provision (benefit)	(241)	106	(2,236)	145	1,450
Ending Balance	12,099	11,607	12,099	11,607	12,944
Consumer [Member]
Loans and Leases Receivable Disclosure [Line Items]
Beginning Balance	8,341	7,718	8,375	8,227	8,227
Charge-offs	(153)	(198)	(360)	(472)	(1,084)
Recoveries	462	406	719	707	1,431
Provision (benefit)	(98)	(789)	(182)	(1,325)	(199)
Ending Balance	8,552	7,137	8,552	7,137	8,375
Consumer [Member] \| Home Equity Lines of Credit [Member]
Loans and Leases Receivable Disclosure [Line Items]
Beginning Balance	6,015	5,412	6,042	5,800	5,800
Charge-offs		(24)		(104)	(277)
Recoveries	183	317	278	526	846
Provision (benefit)	(339)	(657)	(461)	(1,174)	(327)
Ending Balance	5,859	5,048	5,859	5,048	6,042
Commercial Portfolio Segment [Member]
Loans and Leases Receivable Disclosure [Line Items]
Beginning Balance	6,078	6,392	6,090	6,512	6,512
Charge-offs	(138)	(54)	(657)	(259)	(1,188)
Recoveries	85	80	253	130	541
Provision (benefit)	720	(40)	1,059	(5)	225
Ending Balance	6,745	6,378	6,745	6,378	6,090
Construction [Member]
Loans and Leases Receivable Disclosure [Line Items]
Beginning Balance	2,815	2,198	2,497	1,826	1,826
Provision (benefit)	81	213	399	585	671
Ending Balance	2,896	2,411	2,896	2,411	2,497
Construction [Member] \| Commercial [Member]
Loans and Leases Receivable Disclosure [Line Items]
Beginning Balance	407	847	663	642	642
Provision (benefit)	(49)	130	(305)	335	21
Ending Balance	358	977	358	977	663
Construction [Member] \| Residential [Member]
Loans and Leases Receivable Disclosure [Line Items]
Beginning Balance	2,408	1,351	1,834	1,184	1,184
Provision (benefit)	130	83	704	250	650
Ending Balance	2,538	1,434	2,538	1,434	1,834
Residential 1-4 Family [Member] \| Mortgage Loans on Real Estate [Member]
Loans and Leases Receivable Disclosure [Line Items]
Beginning Balance	2,500	2,170	2,676	2,317	2,317
Charge-offs	(2)	(51)	(2)	(52)	(77)
Recoveries	3		5
Provision (benefit)	75	(128)	(103)	(274)	436
Ending Balance	2,576	1,991	2,576	1,991	2,676
Home Equity Loans [Member] \| Consumer [Member]
Loans and Leases Receivable Disclosure [Line Items]
Beginning Balance	1,286	1,736	1,540	1,841	1,841
Charge-offs					(24)
Recoveries	171	23	258	37	297
Provision (benefit)	(215)	(227)	(556)	(346)	(574)
Ending Balance	1,242	1,532	1,242	1,532	1,540
Other Consumer [Member] \| Consumer [Member]
Loans and Leases Receivable Disclosure [Line Items]
Beginning Balance	1,040	570	793	586	586
Charge-offs	(153)	(174)	(360)	(368)	(783)
Recoveries	108	66	183	144	288
Provision (benefit)	456	95	835	195	702
Ending Balance	$ 1,451	$ 557	$ 1,451	$ 557	$ 793

Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts.

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Amount of other addition (reduction) in allowance reserve for credit loss.

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Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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