Fair Values of Financial Instruments - Summary of Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Assets:
Assets estimated fair value	$ 148,981	$ 113,371
Liabilities:
Derivative financial instruments	1,151	581
Obligations of other U. S. government agencies [Member]
Assets:
Assets estimated fair value	25,271	26,473
Obligations of state and political subdivisions [Member]
Assets:
Assets estimated fair value	29,924	21,467
Corporate bonds [Member]
Assets:
Assets estimated fair value	15,859	14,824
Residential mortgage-backed securities [Member]
Assets:
Assets estimated fair value	75,917	47,526
Commercial mortgage-backed securities [Member]
Assets:
Assets estimated fair value	1,273	1,989
Equity securities [Member]
Assets:
Assets estimated fair value	737	1,092
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets:
Assets estimated fair value	737	1,092
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Equity securities [Member]
Assets:
Assets estimated fair value	737	1,092
Significant Other Observable Inputs (Level 2) [Member]
Assets:
Assets estimated fair value	127,841	100,748
Liabilities:
Derivative financial instruments	1,151	581
Significant Other Observable Inputs (Level 2) [Member] | Obligations of other U. S. government agencies [Member]
Assets:
Assets estimated fair value	25,271	26,473
Significant Other Observable Inputs (Level 2) [Member] | Obligations of state and political subdivisions [Member]
Assets:
Assets estimated fair value	10,145	11,072
Significant Other Observable Inputs (Level 2) [Member] | Corporate bonds [Member]
Assets:
Assets estimated fair value	15,235	13,688
Significant Other Observable Inputs (Level 2) [Member] | Residential mortgage-backed securities [Member]
Assets:
Assets estimated fair value	75,917	47,526
Significant Other Observable Inputs (Level 2) [Member] | Commercial mortgage-backed securities [Member]
Assets:
Assets estimated fair value	1,273	1,989
Significant Unobservable Inputs (Level3) [Member]
Assets:
Assets estimated fair value	20,403	11,531
Significant Unobservable Inputs (Level3) [Member] | Obligations of state and political subdivisions [Member]
Assets:
Assets estimated fair value	19,779	10,395
Significant Unobservable Inputs (Level3) [Member] | Corporate bonds [Member]
Assets:
Assets estimated fair value	$ 624	$ 1,136