Allowance for Loan Losses - Summary of Activity in Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Loans and Leases Receivable Disclosure [Line Items]
Beginning Balance	$ 32,582	$ 30,323	$ 32,503
Charge-offs	(3,639)	(2,364)	(4,410)
Recoveries	3,363	2,040	2,141
Provision (benefit)	(1,690)	2,583	89
Ending Balance	30,616	32,582	30,323
Commercial
Loans and Leases Receivable Disclosure [Line Items]
Beginning Balance	663
Ending Balance		663
Residential
Loans and Leases Receivable Disclosure [Line Items]
Beginning Balance	1,834
Ending Balance		1,834
Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Beginning Balance	15,620	13,758	14,265
Charge-offs	(748)	(92)	(246)
Recoveries	1,582	68	397
Provision (benefit)	(2,153)	1,886	(658)
Ending Balance	14,301	15,620	13,758
Mortgage Loans on Real Estate \| Commercial
Loans and Leases Receivable Disclosure [Line Items]
Beginning Balance	12,944	11,441	11,517
Charge-offs	(746)	(15)	(186)
Recoveries	1,528	68	397
Provision (benefit)	(1,731)	1,450	(287)
Ending Balance	11,995	12,944	11,441
Consumer
Loans and Leases Receivable Disclosure [Line Items]
Beginning Balance	8,375	8,227	10,310
Charge-offs	(768)	(1,084)	(1,616)
Recoveries	1,256	1,431	1,315
Provision (benefit)	(1,085)	(199)	(1,782)
Ending Balance	7,778	8,375	8,227
Consumer \| Home equity lines of credit
Loans and Leases Receivable Disclosure [Line Items]
Beginning Balance	6,042	5,800	7,044
Charge-offs	0	(277)	(98)
Recoveries	504	846	698
Provision (benefit)	(974)	(327)	(1,844)
Ending Balance	5,572	6,042	5,800
Commercial
Loans and Leases Receivable Disclosure [Line Items]
Beginning Balance	6,090	6,512	5,831
Charge-offs	(2,123)	(1,188)	(1,444)
Recoveries	525	541	428
Provision (benefit)	657	225	1,697
Ending Balance	5,149	6,090	6,512
Construction
Loans and Leases Receivable Disclosure [Line Items]
Beginning Balance	2,497	1,826	2,097
Charge-offs	0	0	(1,104)
Recoveries	0	0	1
Provision (benefit)	891	671	832
Ending Balance	3,388	2,497	1,826
Construction \| Commercial
Loans and Leases Receivable Disclosure [Line Items]
Beginning Balance	663	642	680
Charge-offs	0
Recoveries	0		1
Provision (benefit)	(345)	21	(39)
Ending Balance	318	663	642
Construction \| Residential
Loans and Leases Receivable Disclosure [Line Items]
Beginning Balance	1,834	1,184	1,417
Charge-offs	0		(1,104)
Recoveries	0		0
Provision (benefit)	1,236	650	871
Ending Balance	3,070	1,834	1,184
Residential 1-4 family \| Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Beginning Balance	2,676	2,317	2,748
Charge-offs	(2)	(77)	(60)
Recoveries	54		0
Provision (benefit)	(422)	436	(371)
Ending Balance	2,306	2,676	2,317
Home equity loans \| Consumer
Loans and Leases Receivable Disclosure [Line Items]
Beginning Balance	1,540	1,841	2,644
Charge-offs	(3)	(24)	(332)
Recoveries	431	297	242
Provision (benefit)	(1,357)	(574)	(713)
Ending Balance	611	1,540	1,841
Other \| Consumer
Loans and Leases Receivable Disclosure [Line Items]
Beginning Balance	793	586	622
Charge-offs	(765)	(783)	(1,186)
Recoveries	321	288	375
Provision (benefit)	1,246	702	775
Ending Balance	$ 1,595	$ 793	$ 586

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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