Loans - Summary of Activity in Allowance for Loan and Lease Losses (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Loans and Leases Receivable Disclosure [Line Items]
Beginning balance	$ 3,262	$ 3,093
Loans charged-off	(483)	(124)
Recoveries	239	293
Ending balance	3,018	3,262
Commercial [Member]
Loans and Leases Receivable Disclosure [Line Items]
Beginning balance	1,448	1,369
Loans charged-off	(214)	(1)
Recoveries	217	80
Ending balance	1,451	1,448
Residential [Member]
Loans and Leases Receivable Disclosure [Line Items]
Beginning balance	1,250	1,246
Loans charged-off	(83)
Recoveries	5	4
Ending balance	1,172	1,250
Consumer [Member]
Loans and Leases Receivable Disclosure [Line Items]
Beginning balance	564	478
Loans charged-off	(186)	(123)
Recoveries	17	209
Ending balance	$ 395	$ 564