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Investment with an Unrealized Loss Position (Details) (USD $) In Thousands, unless otherwise specified | Sep. 30, 2013 | Dec. 31, 2012
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Fair Value |  |
Fair Value, Less than 12 Months | $ 1,041,606 | $ 1,099,987
Fair Value, 12 Months or More | 22,373 | 67,438
Fair Value, Total | 1,063,979 | 1,167,425
Unrealized Loss |  |
Unrealized Loss, Less than 12 Months | (31,975) | (5,810)
Unrealized Loss, 12 Months or More | (1,746) | (640)
Unrealized Loss, Total | (33,721) | (6,450)
State and local governments |  |
Fair Value |  |
Fair Value, Less than 12 Months | 405,834 | 102,896
Fair Value, 12 Months or More | 22,373 | 4,533
Fair Value, Total | 428,207 | 107,429
Unrealized Loss |  |
Unrealized Loss, Less than 12 Months | (21,121) | (1,531)
Unrealized Loss, 12 Months or More | (1,746) | (74)
Unrealized Loss, Total | (22,867) | (1,605)
Corporate bonds |  |
Fair Value |  |
Fair Value, Less than 12 Months | 189,130 | 41,856
Fair Value, 12 Months or More | 0 | 0
Fair Value, Total | 189,130 | 41,856
Unrealized Loss |  |
Unrealized Loss, Less than 12 Months | (2,937) | (238)
Unrealized Loss, 12 Months or More | 0 | 0
Unrealized Loss, Total | (2,937) | (238)
Residential mortgage-backed securities |  |
Fair Value |  |
Fair Value, Less than 12 Months | 446,642 | 955,235
Fair Value, 12 Months or More | 0 | 62,905
Fair Value, Total | 446,642 | 1,018,140
Unrealized Loss |  |
Unrealized Loss, Less than 12 Months | (7,917) | (4,041)
Unrealized Loss, 12 Months or More | 0 | (566)
Unrealized Loss, Total | $ (7,917) | $ (4,607)

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- Definition Amount of accumulated pre-tax unrealized loss on securities classified as available-for-sale 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 securities classified as available-for-sale impacting investments. + References No definition available. + Details
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- Definition Amount of accumulated pre-tax unrealized loss on investments in available-forsale 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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