Fair Value Measurements of Assets Recognized in Consolidated Balance Sheets Measured at Fair Value on Recurring Basis (Detail) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
U.S. government agencies
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of asset, recurring basis	$ 27,023	$ 14,380
State and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of asset, recurring basis	3,623	4,946
Equity securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of asset, recurring basis		22
Fair Value, Inputs, Level 1 | U.S. government agencies
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of asset, recurring basis	0	0
Fair Value, Inputs, Level 1 | State and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of asset, recurring basis	0	0
Fair Value, Inputs, Level 1 | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of asset, recurring basis		22
Fair Value, Inputs, Level 2 | U.S. government agencies
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of asset, recurring basis	27,023	14,380
Fair Value, Inputs, Level 2 | State and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of asset, recurring basis	3,623	4,946
Fair Value, Inputs, Level 2 | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of asset, recurring basis		0
Fair Value, Inputs, Level 3 | U.S. government agencies
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of asset, recurring basis	0	0
Fair Value, Inputs, Level 3 | State and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of asset, recurring basis	$ 0	0
Fair Value, Inputs, Level 3 | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of asset, recurring basis		$ 0