Fair Value of Financial Instruments - Impaired Loans and Other Real Estate (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Collateral Dependent Impaired Loans [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a nonrecurring basis, Total	$ 195	$ 215
Other Real Estate Owned-Commercial [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a nonrecurring basis, Total	29
Fair Value on Nonrecurring Basis [Member] | Collateral Dependent Impaired Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a nonrecurring basis, Total	195	215
Fair Value on Nonrecurring Basis [Member] | Collateral Dependent Impaired Loans [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a nonrecurring basis, Total	195	$ 215
Fair Value on Nonrecurring Basis [Member] | Other Real Estate Owned-Commercial [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a nonrecurring basis, Total	29
Fair Value on Nonrecurring Basis [Member] | Other Real Estate Owned-Commercial [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a nonrecurring basis, Total	$ 29