Allowance for Loan Losses - Summary of Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Allowance for Loan Losses:
Allowance for loan losses, beginning of year	$ 29,070	$ 27,144		$ 28,543	$ 26,255
Charge-offs	(118)	(89)		(336)	(247)
Recoveries	70	1,490		190	1,637
Provision	75			700	900
Allowance for loan losses, end of year	29,097	28,545	$ 27,144	29,097	28,545
Amount of allowance for loan losses for loans deemed to be impaired	88	538		88	538
Amount of allowance for loan losses for loans not deemed to be impaired	29,009	28,007		29,009	28,007
Loans:
Total loans, net	2,375,661	2,261,339		2,375,661	2,261,339	$ 2,285,578
Loans deemed to be impaired	2,576	6,015		2,576	6,015
Loans not deemed to be impaired	2,373,085	2,255,324		2,373,085	2,255,324
Construction and Land Development [Member]
Allowance for Loan Losses:
Allowance for loan losses, beginning of year	1,052	633		1,092	1,645
Recoveries		1,432			1,432
Provision	(752)	(1,155)		(792)	(2,167)
Allowance for loan losses, end of year	300	910	633	300	910
Amount of allowance for loan losses for loans not deemed to be impaired	300	910		300	910
Loans:
Total loans, net	7,824	12,434		7,824	12,434	13,628
Loans not deemed to be impaired	7,824	12,434		7,824	12,434
Commercial and Industrial [Member]
Allowance for Loan Losses:
Allowance for loan losses, beginning of year	11,338	10,384		10,998	9,651
Charge-offs	(57)	(11)		(108)	(16)
Recoveries	23	16		49	49
Provision	9	895		374	1,600
Allowance for loan losses, end of year	11,313	11,284	10,384	11,313	11,284
Amount of allowance for loan losses for loans deemed to be impaired	2	93		2	93
Amount of allowance for loan losses for loans not deemed to be impaired	11,311	11,191		11,311	11,191
Loans:
Total loans, net	783,950	783,960		783,950	783,960	761,625
Loans deemed to be impaired	203	660		203	660
Loans not deemed to be impaired	783,747	783,300		783,747	783,300
Municipal [Member]
Allowance for Loan Losses:
Allowance for loan losses, beginning of year	1,832	1,704		1,838	1,720
Provision	751	84		745	68
Allowance for loan losses, end of year	2,583	1,788	1,704	2,583	1,788
Amount of allowance for loan losses for loans not deemed to be impaired	2,583	1,788		2,583	1,788
Loans:
Total loans, net	121,802	94,532		121,802	94,532	97,290
Loans not deemed to be impaired	121,802	94,532		121,802	94,532
Commercial Real Estate [Member]
Allowance for Loan Losses:
Allowance for loan losses, beginning of year	10,848	10,209		10,663	9,728
Provision	53	415		238	896
Allowance for loan losses, end of year	10,901	10,624	10,209	10,901	10,624
Amount of allowance for loan losses for loans deemed to be impaired	86	95		86	95
Amount of allowance for loan losses for loans not deemed to be impaired	10,815	10,529		10,815	10,529
Loans:
Total loans, net	765,385	730,265		765,385	730,265	750,362
Loans deemed to be impaired	2,373	2,680		2,373	2,680
Loans not deemed to be impaired	763,012	727,585		763,012	727,585
Residential Real Estate [Member]
Allowance for Loan Losses:
Allowance for loan losses, beginning of year	2,210	2,493		2,190	1,873
Provision	(24)	(182)		(4)	438
Allowance for loan losses, end of year	2,186	2,311	2,493	2,186	2,311
Amount of allowance for loan losses for loans deemed to be impaired		350			350
Amount of allowance for loan losses for loans not deemed to be impaired	2,186	1,961		2,186	1,961
Loans:
Total loans, net	364,317	335,114		364,317	335,114	348,250
Loans deemed to be impaired		2,675			2,675
Loans not deemed to be impaired	364,317	332,439		364,317	332,439
Consumer [Member]
Allowance for Loan Losses:
Allowance for loan losses, beginning of year	380	336		365	373
Charge-offs	(61)	(78)		(228)	(231)
Recoveries	47	42		141	156
Provision	(84)	32		4	34
Allowance for loan losses, end of year	282	332	336	282	332
Amount of allowance for loan losses for loans not deemed to be impaired	282	332		282	332
Loans:
Total loans, net	21,748	21,216		21,748	21,216	22,083
Loans not deemed to be impaired	21,748	21,216		21,748	21,216
Home Equity [Member]
Allowance for Loan Losses:
Allowance for loan losses, beginning of year	1,120	1,078		1,111	989
Provision	(33)	(28)		(24)	61
Allowance for loan losses, end of year	1,087	1,050	1,078	1,087	1,050
Amount of allowance for loan losses for loans not deemed to be impaired	1,087	1,050		1,087	1,050
Loans:
Total loans, net	310,635	283,818		310,635	283,818	$ 292,340
Loans not deemed to be impaired	310,635	283,818		310,635	283,818
Unallocated [Member]
Allowance for Loan Losses:
Allowance for loan losses, beginning of year	290	307		286	276
Provision	155	(61)		159	(30)
Allowance for loan losses, end of year	445	$ 246	307	445	246
Amount of allowance for loan losses for loans not deemed to be impaired	445		$ 246	445	$ 246
Loans:
Total loans, net	$ 2,375,661			$ 2,375,661

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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