Allowance for Loan Losses - Loans Evaluated for Impairment Individually and Collectively by Loan Type (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans individually evaluated for impairment	$ 1,157	$ 1,094
Loans collectively evaluated for impairment	6,745	6,676
Purchased credit-impaired loans	0	0
Total allowance on loan losses	7,902	7,770	$ 3,863
Loans individually evaluated for impairment	7,606	9,107
Loans collectively evaluated for impairment	889,416	751,364
Purchased credit-impaired loans	5,323	5,825
Total Loans	902,345	766,296
Mortgage Loans on Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans individually evaluated for impairment	1,036	861
Loans collectively evaluated for impairment	3,931	3,003
Purchased credit-impaired loans	0	0
Total allowance on loan losses	4,967	3,864	3,318
Loans individually evaluated for impairment	7,485	8,874
Loans collectively evaluated for impairment	701,235	595,007
Purchased credit-impaired loans	5,277	5,756
Total Loans	713,997	609,637
Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans individually evaluated for impairment		92
Loans collectively evaluated for impairment	1,374	786
Purchased credit-impaired loans	0	0
Total allowance on loan losses	1,374	878	493
Loans individually evaluated for impairment		92
Loans collectively evaluated for impairment	164,608	114,001
Total Loans	164,608	114,093
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans individually evaluated for impairment	121	141
Loans collectively evaluated for impairment	1,440	2,887
Purchased credit-impaired loans	0	0
Total allowance on loan losses	1,561	3,028	$ 52
Loans individually evaluated for impairment	121	141
Loans collectively evaluated for impairment	23,573	42,356
Purchased credit-impaired loans	46	69
Total Loans	$ 23,740	$ 42,566