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Securities - Summary of Investments in an Unrealized Loss Position that were Temporarily Impaired (Detail) (USD $) In Thousands, unless otherwise specified | Sep. 30, 2013 | Dec. 31, 2012
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Summary of investments in unrealized loss position that were temporarily impaired |  |
Less than 12 months - Fair Value | $ 58,243 | $ 23,899
12 months or more - Fair Value | 8,295 |
Total - Fair Value | 66,538 | 23,899
Summary of investments in unrealized loss position that were temporarily impaired, Unrealized (Loss) |  |
Less than 12 months - Unrealized (Loss) | (2,198) | (319)
12 months or more - Unrealized (Loss) | (351) |
Total Unrealized (Loss) | (2,549) | (319)
U.S. Agency and Mortgage-Backed Securities [Member] |  |
Summary of investments in unrealized loss position that were temporarily impaired |  |
Less than 12 months - Fair Value | 50,796 | 19,612
12 months or more - Fair Value | 5,877 |
Total - Fair Value | 56,673 | 19,612
Summary of investments in unrealized loss position that were temporarily impaired, Unrealized (Loss) |  |
Less than 12 months - Unrealized (Loss) | (1,753) | (236)
12 months or more - Unrealized (Loss) | (196) |
Total Unrealized (Loss) | (1,949) | (236)
Obligations of States and Political Subdivisions [Member] |  |
Summary of investments in unrealized loss position that were temporarily impaired |  |
Less than 12 months - Fair Value | 7,447 | 4,287
12 months or more - Fair Value | 2,418 |
Total - Fair Value | 9,865 | 4,287
Summary of investments in unrealized loss position that were temporarily impaired, Unrealized (Loss) |  |
Less than 12 months - Unrealized (Loss) | (445) | (83)
12 months or more - Unrealized (Loss) | (155) |
Total Unrealized (Loss) | $ (600) | $ (83)

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- Definition Amount of accumulated pre-tax unrealized loss on investments in available-for-sale securities that have been in a loss position for twelve months or longer impacting investments. + References No definition available. + Details
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- Definition Amount of accumulated pre-tax unrealized loss on investments on securities classified as available-for-sale securities impacting investments. + References No definition available. + Details
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- Definition Amount of accumulated pre-tax unrealized loss on investments in available-for-sale securities that have been in a loss position for less than twelve months impacting investments. + References No definition available. + Details
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- Definition This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563 + Details
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- Definition This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for less than twelve months. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27337-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563 + Details
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- Definition This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for twelve months or longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27337-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563 + Details
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