Allowance for Loan Losses - Summary of Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Allowance for Loan Losses:
Allowance for loan losses, beginning of year	$ 28,543	$ 26,255
Charge-offs	(142)	(87)
Recoveries	72	77
Provision	375	450
Allowance for loan losses, end of year	28,848	26,695
Amount of allowance for loan losses for loans deemed to be impaired	100	686	$ 145
Amount of allowance for loan losses for loans not deemed to be impaired	28,748	26,009
Loans:
Total loans, net	2,310,660	2,187,147	2,285,578
Loans deemed to be impaired	3,266	5,824	3,051
Loans not deemed to be impaired	2,307,394	2,181,323
Construction and Land Development [Member]
Allowance for Loan Losses:
Allowance for loan losses, beginning of year	1,092	1,645
Provision	(81)	(207)
Allowance for loan losses, end of year	1,011	1,438
Amount of allowance for loan losses for loans not deemed to be impaired	1,011	1,438
Loans:
Total loans, net	13,305	17,583	13,628
Loans not deemed to be impaired	13,305	17,583
Commercial and Industrial [Member]
Allowance for Loan Losses:
Allowance for loan losses, beginning of year	10,998	9,651
Charge-offs	(43)	(5)
Recoveries	18	23
Provision	183	(5)
Allowance for loan losses, end of year	11,156	9,664
Amount of allowance for loan losses for loans deemed to be impaired	6	12	54
Amount of allowance for loan losses for loans not deemed to be impaired	11,150	9,652
Loans:
Total loans, net	767,436	758,621	761,625
Loans deemed to be impaired	320	522	401
Loans not deemed to be impaired	767,116	758,099
Municipal [Member]
Allowance for Loan Losses:
Allowance for loan losses, beginning of year	1,838	1,720
Provision	160
Allowance for loan losses, end of year	1,998	1,720
Amount of allowance for loan losses for loans not deemed to be impaired	1,998	1,720
Loans:
Total loans, net	105,288	104,044	97,290
Loans not deemed to be impaired	105,288	104,044
Commercial Real Estate [Member]
Allowance for Loan Losses:
Allowance for loan losses, beginning of year	10,663	9,728
Provision	104	59
Allowance for loan losses, end of year	10,767	9,787
Amount of allowance for loan losses for loans deemed to be impaired	94	94	91
Amount of allowance for loan losses for loans not deemed to be impaired	10,673	9,693
Loans:
Total loans, net	746,703	726,440	750,362
Loans deemed to be impaired	2,946	2,528	2,650
Loans not deemed to be impaired	743,757	723,912
Residential Real Estate [Member]
Allowance for Loan Losses:
Allowance for loan losses, beginning of year	2,190	1,873
Provision	(55)	586
Allowance for loan losses, end of year	2,135	2,459
Amount of allowance for loan losses for loans deemed to be impaired		580
Amount of allowance for loan losses for loans not deemed to be impaired	2,135	1,879
Loans:
Total loans, net	349,966	300,941	348,250
Loans deemed to be impaired		2,774
Loans not deemed to be impaired	349,966	298,167
Consumer [Member]
Allowance for Loan Losses:
Allowance for loan losses, beginning of year	365	373
Charge-offs	(99)	(82)
Recoveries	54	54
Provision	22	(24)
Allowance for loan losses, end of year	342	321
Amount of allowance for loan losses for loans not deemed to be impaired	342	321
Loans:
Total loans, net	22,123	19,339	22,083
Loans not deemed to be impaired	22,123	19,339
Home Equity [Member]
Allowance for Loan Losses:
Allowance for loan losses, beginning of year	1,111	989
Provision	(10)	78
Allowance for loan losses, end of year	1,101	1,067
Amount of allowance for loan losses for loans not deemed to be impaired	1,101	1,067
Loans:
Total loans, net	305,839	260,179	$ 292,340
Loans not deemed to be impaired	305,839	260,179
Unallocated [Member]
Allowance for Loan Losses:
Allowance for loan losses, beginning of year	286	276
Provision	52	(37)
Allowance for loan losses, end of year	338	239
Amount of allowance for loan losses for loans not deemed to be impaired	$ 338	$ 239

Amount of allowance for loans losses for loans not deemed to be impaired.

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Provision for loan losses gains expensed.

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

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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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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The recorded amount of loans and debt securities, with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it was probable, at acquisition, that the investor would be unable to collect all contractually required payments receivable, but which are not deemed to be impaired since the acquisition by transfer. Therefore, no allowance for credit losses is recorded.

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Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

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Amount of allowance for credit losses related to recorded investment.

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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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Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

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