Loans - Schedule of Allowances for Loan Losses by Portfolio Segment (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 7,017	$ 5,907
Provision for loan losses	178	285
Charge-offs	(87)	(70)
Recoveries	12	165
Net (charge-offs) recoveries	(75)	95
Ending balance	7,120	6,287
Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	2,408	2,178
Provision for loan losses	212	(339)
Charge-offs	(15)	(5)
Recoveries	4	163
Net (charge-offs) recoveries	(11)	158
Ending balance	2,609	1,997
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	2,153	1,791
Provision for loan losses	147	17
Ending balance	2,300	1,808
Residential Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,152	1,245
Provision for loan losses	209	(24)
Charge-offs	(15)
Recoveries	1	1
Net (charge-offs) recoveries	(14)	1
Ending balance	1,347	1,222
Construction & Land Development [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	203	258
Provision for loan losses	52	(88)
Ending balance	255	170
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	481	306
Provision for loan losses	87	83
Charge-offs	(57)	(65)
Recoveries	7	1
Net (charge-offs) recoveries	(50)	(64)
Ending balance	518	325
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	620	129
Provision for loan losses	(529)	636
Ending balance	$ 91	$ 765