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Adoption of Accounting Pronouncements (Income Statement Statement) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified | 3 Months Ended | 12 Months Ended
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Dec. 31, 2011 | Sep. 30, 2011 | Jun. 30, 2011 | Mar. 31, 2011 | Dec. 31, 2010 | Sep. 30, 2010 | Jun. 30, 2010 | Mar. 31, 2010 | Dec. 31, 2011 | Dec. 31, 2010 | Dec. 31, 2009
Underwriting (loss) profit | $ 4,971 | $ (68,124) | $ (32,682) | $ (11,084) | $ (468) | $ (3,933) | $ (3,161) | $ (14,605) | $ (106,919) | $ (22,167) | $ 2,385
Net income | 16,133 | (20,142) | 2,325 | 21,549 | 23,775 | 17,197 | 18,766 | 5,803 | 19,865 | 65,541 | 36,398
Combined ratio |  |  |  |  |  |  |  |  | 107.40% | 101.60% | 99.80%
Basic net income per share | $ 0.30 | $ (0.37) | $ 0.04 | $ 0.40 | $ 0.44 | $ 0.32 | $ 0.35 | $ 0.11 | $ 0.37 | $ 1.23 | $ 0.69
Diluted net income per share | $ 0.29 | $ (0.37) | $ 0.04 | $ 0.39 | $ 0.43 | $ 0.32 | $ 0.35 | $ 0.11 | $ 0.36 | $ 1.20 | $ 0.68
Retrospective Effect Of Change In Accounting Principle As Reported [Member] |  |  |  |  |  |  |  |  |  |  |
Underwriting (loss) profit |  |  |  |  |  |  |  |  | (106,919) | (22,167) | 2,385
Net income |  |  |  |  |  |  |  |  | 19,865 | 65,541 | 36,398
Combined ratio |  |  |  |  |  |  |  |  | 107.40% | 101.60% | 99.80%
Basic net income per share |  |  |  |  |  |  |  |  | $ 0.37 | $ 1.23 | $ 0.69
Diluted net income per share |  |  |  |  |  |  |  |  | $ 0.36 | $ 1.20 | $ 0.68
Retrospective Effect Of Change In Accounting Principle As Restated [Member] |  |  |  |  |  |  |  |  |  |  |
Underwriting (loss) profit |  |  |  |  |  |  |  |  | (103,584) | (19,974) | 2,111
Net income |  |  |  |  |  |  |  |  | $ 22,033 | $ 66,966 | $ 36,220
Combined ratio |  |  |  |  |  |  |  |  | 107.20% | 101.40% | 99.90%
Basic net income per share |  |  |  |  |  |  |  |  | $ 0.41 | $ 1.26 | $ 0.69
Diluted net income per share |  |  |  |  |  |  |  |  | $ 0.40 | $ 1.23 | $ 0.68

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- Definition The GAAP combined ratio (expressed as a percentage) is a calculation wherein the sum of: (i) loss and loss adjustment expenses (ii) underwriting expenses and (iii) dividends to policyholders is divided by net premiums earned. + References No definition available. + Details
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