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Fair Value of Instruments - Changes in the Level 3 Fair Value Category of Unobservable Inputs (Detail) (USD $) In Thousands, unless otherwise specified | 3 Months Ended |  |  |  |  | 3 Months Ended
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Mar. 31, 2013 | Mar. 31, 2014 | Dec. 31, 2013 | Mar. 31, 2014 State and local governments [Member] | Dec. 31, 2013 State and local governments [Member] | Mar. 31, 2014 Unobservable Inputs (Level 3) [Member] State and local governments [Member] | Mar. 31, 2013 Unobservable Inputs (Level 3) [Member] State and local governments [Member] | Mar. 31, 2014 Unobservable Inputs (Level 3) [Member] State and local governments [Member] Tax - Exempt [Member] | Mar. 31, 2013 Unobservable Inputs (Level 3) [Member] State and local governments [Member] Tax - Exempt [Member] | Mar. 31, 2014 Unobservable Inputs (Level 3) [Member] State and local governments [Member] Taxable [Member] | Mar. 31, 2013 Unobservable Inputs (Level 3) [Member] State and local governments [Member] Taxable [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |  |  |  |  |  |  |  |  |  |
Beginning Balance |  | $ 307,725 | $ 324,509 | $ 79,815 | $ 81,473 | $ 10,346 | $ 16,408 | $ 8,802 | $ 14,863 | $ 1,544 | $ 1,545
Change in Market Value |  |  |  |  |  | (1,490) | (530) | (1,121) | (504) | (369) | (26)
Purchases | 54,850 |  |  |  |  |  | 519 |  | 519 |  |
Payments & Maturities |  |  |  |  |  | (200) | (4,388) | (200) | (4,388) |  |
Ending Balance |  | $ 307,725 | $ 324,509 | $ 79,815 | $ 81,473 | $ 8,656 | $ 12,009 | $ 7,481 | $ 10,490 | $ 1,175 | $ 1,519

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- Definition Payments And Maturities Of Available For Sale Securities + References No definition available. + Details
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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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- Definition The cash outflow to acquire debt and equity securities not classified as either held-to-maturity securities or trading securities which would be classified as available-for-sale securities and reported at fair value, with unrealized gains and losses excluded from earnings and reported in a separate component of shareholders' equity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Investing Activities -URI http://asc.fasb.org/extlink&oid=6516133 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26853-111562 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 13 -Subparagraph (a),(b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3213-108585 + Details
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