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Adoption of Accounting Pronouncements (Balance Sheet Information) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified | Dec. 31, 2011 | Dec. 31, 2010 | Dec. 31, 2009
--- | --- | --- | ---
Deferred policy acquisition costs | $ 214,069 | $ 209,627 |
Total assets | 5,736,369 | 5,231,772 |
Stockholders' Equity | 1,109,228 | 1,071,109 | 1,002,375
Retrospective Effect Of Change In Accounting Principle As Reported [Member] |  |  |
Deferred policy acquisition costs | 214,069 | 209,627 |
Total assets | 5,736,369 | 5,231,772 |
Stockholders' Equity | 1,109,228 | 1,071,109 |
Book value per share | $ 20.39 | $ 19.95 |
Retrospective Effect Of Change In Accounting Principle As Restated [Member] |  |  |
Deferred policy acquisition costs | 135,761 | 127,984 |
Total assets | 5,685,469 | 5,178,704 |
Stockholders' Equity | $ 1,058,328 | $ 1,018,041 |
Book value per share | $ 19.45 | $ 18.97 |

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