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, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
U.S. government agencies
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of asset, recurring basis	$ 24,070	$ 64,168
State and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of asset, recurring basis	10,759	17,817
Equity securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of asset, recurring basis	24	13
Fair Value, Inputs, Level 1 | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of asset, recurring basis	24	13
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	24,070	64,168
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	$ 10,759	$ 17,817