Fair Value Measurements - Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Fair Value Measurements Disclosure [Line Items]
Securities available for sale/Available-for-sale, Fair value	$ 356,382	$ 343,018
Equity Securities [Member]
Fair Value Measurements Disclosure [Line Items]
Securities available for sale/Available-for-sale, Fair value	28	28
Other Investments [Member]
Fair Value Measurements Disclosure [Line Items]
Securities available for sale/Available-for-sale, Fair value	11,695	11,748
Fair Value, Measurements, Recurring [Member]
Fair Value Measurements Disclosure [Line Items]
Securities available for sale/Available-for-sale, Fair value	356,382	343,018
Fair Value, Measurements, Recurring [Member] | Debt Securities [Member]
Fair Value Measurements Disclosure [Line Items]
Securities available for sale/Available-for-sale, Fair value	344,659	331,242
Fair Value, Measurements, Recurring [Member] | Other Investments [Member]
Fair Value Measurements Disclosure [Line Items]
Securities available for sale/Available-for-sale, Fair value	11,695	11,748
Fair Value, Measurements, Recurring [Member] | Common Stock [Member] | Equity Securities [Member]
Fair Value Measurements Disclosure [Line Items]
Securities available for sale/Available-for-sale, Fair value	28	28
Fair Value, Measurements, Recurring [Member] | States and Political Subdivisions [Member] | Debt Securities [Member]
Fair Value Measurements Disclosure [Line Items]
Securities available for sale/Available-for-sale, Fair value	173,163	157,374
Fair Value, Measurements, Recurring [Member] | U.S. Agency-Based Mortgage-Backed Securities [Member] | Debt Securities [Member]
Fair Value Measurements Disclosure [Line Items]
Securities available for sale/Available-for-sale, Fair value	7,443	8,498
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Debt Securities [Member]
Fair Value Measurements Disclosure [Line Items]
Securities available for sale/Available-for-sale, Fair value	164,053	165,370
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value Measurements Disclosure [Line Items]
Securities available for sale/Available-for-sale, Fair value	28	28
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Common Stock [Member] | Equity Securities [Member]
Fair Value Measurements Disclosure [Line Items]
Securities available for sale/Available-for-sale, Fair value	28	28
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value Measurements Disclosure [Line Items]
Securities available for sale/Available-for-sale, Fair value	344,659	331,242
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Debt Securities [Member]
Fair Value Measurements Disclosure [Line Items]
Securities available for sale/Available-for-sale, Fair value	344,659	331,242
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | States and Political Subdivisions [Member] | Debt Securities [Member]
Fair Value Measurements Disclosure [Line Items]
Securities available for sale/Available-for-sale, Fair value	173,163	157,374
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | U.S. Agency-Based Mortgage-Backed Securities [Member] | Debt Securities [Member]
Fair Value Measurements Disclosure [Line Items]
Securities available for sale/Available-for-sale, Fair value	7,443	8,498
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Debt Securities [Member]
Fair Value Measurements Disclosure [Line Items]
Securities available for sale/Available-for-sale, Fair value	164,053	165,370
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value Measurements Disclosure [Line Items]
Securities available for sale/Available-for-sale, Fair value	11,695	11,748
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Other Investments [Member]
Fair Value Measurements Disclosure [Line Items]
Securities available for sale/Available-for-sale, Fair value	$ 11,695	$ 11,748