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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Loans - Summary of Major Classifications of Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016
Loans and Leases Receivable Disclosure [Line Items]
Loans, gross	$ 372,700		$ 333,710
Net deferred loan fees	515		589
Allowance for loan and lease losses	(3,242)	$ (3,092)	(3,093)	$ (3,069)	$ (3,048)	$ (3,008)
Loans, net	369,973		331,206
Commercial [Member] \| Real Estate [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans, gross	184,953		156,991
Commercial [Member] \| Land [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans, gross	2,169		2,687
Commercial [Member] \| Other Commercial Loan [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans, gross	32,846		19,715
Residential Real Estate [Member] \| First Mortgage [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans, gross	108,061		106,120
Residential Real Estate [Member] \| Construction Loans [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans, gross	4,785		3,358
Consumer [Member] \| Home Equity Lines Of Credit [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans, gross	37,850		42,344
Consumer [Member] \| Other Consumer Loan [Member]
Loans and Leases Receivable Disclosure [Line Items]
Loans, gross	$ 2,036		$ 2,495