Loans - Recorded Investment for Consumer Loans, Credit Quality based on Status of Loan and Payment Activity (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	$ 1,101,963	$ 846,374	$ 834,737
Performing	2,389	116	121
Consumer - Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Performing	3,875	3,928
Consumer - Credit [Member] | Performing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Performing	3,861	3,909
Consumer - Credit [Member] | Nonperforming [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Performing	14	19
Consumer - Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Performing	43,821	38,127
Consumer - Other [Member] | Performing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Performing	43,366	38,073
Consumer - Other [Member] | Nonperforming [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Performing	455	54
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	160,489	80,232	84,052
Performing	346	116	$ 121
Pass [Member] | Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	158,309	79,121
5 [Member] | Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	135	232
6 [Member] | Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans after net deferred loan fees and costs	$ 2,045	$ 879