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Fair Value Measurements - Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified | Sep. 30, 2013 | Dec. 31, 2012
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Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair Value | $ 10,271 |
Securities available for sale/Available-for-sale, Fair Value | 225,232 | 155,905
Equity Securities [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair Value | 12,260 | 6,766
Fair Value, Measurements, Recurring [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair Value | 225,232 | 155,905
Fair Value, Measurements, Recurring [Member] | Other Investment [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair Value | 10,271 |
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] | Common Stock |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair Value | 12,260 | 6,766
Fair Value, Measurements, Recurring [Member] | Debt Securities [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair Value | 202,701 | 149,139
Fair Value, Measurements, Recurring [Member] | Debt Securities [Member] | States and political subdivisions [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair Value | 130,558 | 98,242
Fair Value, Measurements, Recurring [Member] | Debt Securities [Member] | Corporate bonds [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair Value | 64,102 | 39,810
Fair Value, Measurements, Recurring [Member] | Debt Securities [Member] | U.S. agency-based mortgage-backed securities [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair Value | 8,041 | 11,087
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 | 12,260 | 6,766
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Other Investment [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair Value |  |
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] | Common Stock |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair Value | 12,260 | 6,766
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Debt Securities [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair Value |  |
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Debt Securities [Member] | States and political subdivisions [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair Value |  |
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Debt Securities [Member] | Corporate bonds [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair Value |  |
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Debt Securities [Member] | U.S. agency-based mortgage-backed securities [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair Value |  |
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 | 202,701 | 149,139
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Other Investment [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair Value |  |
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] | Common Stock |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair Value |  |
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 | 202,701 | 149,139
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Debt Securities [Member] | States and political subdivisions [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair Value | 130,558 | 98,242
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Debt Securities [Member] | Corporate bonds [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair Value | 64,102 | 39,810
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Debt Securities [Member] | U.S. agency-based mortgage-backed securities [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair Value | 8,041 | 11,087
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 | 10,271 |
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Other Investment [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair Value | 10,271 |
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities [Member] | Common Stock |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair Value |  |
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Debt Securities [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair Value |  |
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Debt Securities [Member] | States and political subdivisions [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair Value |  |
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Debt Securities [Member] | Corporate bonds [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair Value |  |
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Debt Securities [Member] | U.S. agency-based mortgage-backed securities [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair Value |  |

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