Fair Value Measurement - Assets and Liabilities Measured at Fair Value (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	$ 231,013	$ 230,230
(Level 2) [Member] | Assets Measured at Fair Value on a Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	231,013	230,230
(Level 2) [Member] | Assets Measured at Fair Value on a Recurring Basis [Member] | Swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value swap asset	2,375	1,560
Fair value swap liability	2,375	1,560
(Level 2) [Member] | Assets Measured at Fair Value on a Recurring Basis [Member] | U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	29,399	30,358
(Level 2) [Member] | Assets Measured at Fair Value on a Recurring Basis [Member] | Obligations of States and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	117,648	118,056
(Level 2) [Member] | Assets Measured at Fair Value on a Recurring Basis [Member] | Mortgage-backed Securities in Government Sponsored Entities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total securities available for sale	83,966	81,816
(Level 2) [Member] | Assets Measured at Fair Value on a Recurring Basis [Member] | Equity Securities in Financial Institutions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	907	832
(Level 3) [Member] | Assets Measured at Fair Value on a Nonrecurring Basis [Member] | Impaired Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	$ 1,350	1,040
(Level 3) [Member] | Assets Measured at Fair Value on a Nonrecurring Basis [Member] | Other Real Estate Owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets		$ 16