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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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Allowance for Loans Losses - Summary of allowance for loans losses (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Financing Receivable, Impaired [Line Items]
Allowance, beginning of period			$ 3,580	$ 2,803	$ 2,803
Charge-Offs			779		564
Recoveries			(138)		(116)
Net charge-offs (recoveries)			641		448
Provision for loan losses	$ 570	$ 225	1,465	$ 640	1,225
Allowance, end of period	$ 4,404		4,404		3,580
Commercial and industrial [Member]
Financing Receivable, Impaired [Line Items]
Charge-Offs			43		6
Real estate, mortgage [Member]
Financing Receivable, Impaired [Line Items]
Charge-Offs			3		13
Recoveries			(6)		(12)
Consumer and other loans [Member]
Financing Receivable, Impaired [Line Items]
Charge-Offs			733		545
Recoveries			$ (132)		$ (104)