Allowance for Loan Losses - Loans Evaluated for Impairment Individually and Collectively by Type (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans individually evaluated for impairment	$ 1,106		$ 1,157
Loans collectively evaluated for impairment	6,373		6,745
Purchased credit-impaired loans	0		0
Total allowance for loan losses	7,479	$ 7,858	7,902	$ 7,113	$ 7,923	$ 7,770
Loans individually evaluated for impairment	7,477		7,606
Loans collectively evaluated for impairment	905,092		889,416
Purchased credit-impaired loans	5,098		5,323
Total Loans	917,667		902,345
Mortgage Loans on Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans individually evaluated for impairment	987		1,036
Loans collectively evaluated for impairment	4,065		3,931
Purchased credit-impaired loans	0		0
Total allowance for loan losses	5,052	5,259	4,967	4,244	4,190	3,864
Loans individually evaluated for impairment	7,358		7,485
Loans collectively evaluated for impairment	700,837		701,235
Purchased credit-impaired loans	5,052		5,277
Total Loans	713,247		713,997
Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans collectively evaluated for impairment	1,537		1,374
Purchased credit-impaired loans	0		0
Total allowance for loan losses	1,537	1,406	1,374	944	1,043	878
Loans collectively evaluated for impairment	187,531		164,608
Total Loans	187,531		164,608
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans individually evaluated for impairment	119		121
Loans collectively evaluated for impairment	771		1,440
Purchased credit-impaired loans	0		0
Total allowance for loan losses	890	$ 1,193	1,561	$ 1,925	$ 2,690	$ 3,028
Loans individually evaluated for impairment	119		121
Loans collectively evaluated for impairment	16,724		23,573
Purchased credit-impaired loans	46		46
Total Loans	$ 16,889		$ 23,740