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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 | Jun. 30, 2013 | Dec. 31, 2012
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Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair Value | $ 212,872 | $ 155,905
Equity Securities [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair Value | 13,498 | 6,766
Fair Value, Measurements, Recurring [Member] |  |
Fair Value Measurements Disclosure [Line Items] |  |
Securities available for sale/Available-for-sale, Fair Value | 212,872 | 155,905
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 | 13,498 | 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 | 199,374 | 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 | 132,265 | 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 | 58,670 | 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 | 8,439 | 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 | 13,498 | 6,766
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 | 13,498 | 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 | 199,374 | 149,139
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 | 199,374 | 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 | 132,265 | 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 | 58,670 | 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 | 8,439 | 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 |  |
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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- Definition Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562 + Details
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