Fair Value Measurements - Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Fair Value Measurements Disclosure [Line Items]
Securities available for sale/Available-for-sale, Fair value	$ 299,685	$ 257,770
Equity securities [Member]
Fair Value Measurements Disclosure [Line Items]
Securities available for sale/Available-for-sale, Fair value	3,980	9,302
Other investments [Member]
Fair Value Measurements Disclosure [Line Items]
Securities available for sale/Available-for-sale, Fair value	11,092	10,591
Fair Value, Measurements, Recurring [Member]
Fair Value Measurements Disclosure [Line Items]
Securities available for sale/Available-for-sale, Fair value	299,685	257,770
Fair Value, Measurements, Recurring [Member] | Debt Securities [Member]
Fair Value Measurements Disclosure [Line Items]
Securities available for sale/Available-for-sale, Fair value	284,613	237,877
Fair Value, Measurements, Recurring [Member] | Other investments [Member]
Fair Value Measurements Disclosure [Line Items]
Securities available for sale/Available-for-sale, Fair value	11,092	10,591
Fair Value, Measurements, Recurring [Member] | Common stock | Equity securities [Member]
Fair Value Measurements Disclosure [Line Items]
Securities available for sale/Available-for-sale, Fair value	3,980	9,302
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	155,092	150,375
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	121,763	80,428
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	7,758	7,074
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	3,980	9,302
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Common stock | Equity securities [Member]
Fair Value Measurements Disclosure [Line Items]
Securities available for sale/Available-for-sale, Fair value	3,980	9,302
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	284,613	237,877
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	284,613	237,877
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	155,092	150,375
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	121,763	80,428
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	7,758	7,074
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	11,092	10,591
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	$ 11,092	$ 10,591