Fair Value of Instruments - Impaired Loans and Other Real Estate (Detail) - Fair Value on Nonrecurring Basis [Member] - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
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	$ 577	$ 576
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		144
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	577	720
Level 3 [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	$ 577	576
Level 3 [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		$ 144