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Significant Transactions (Details 3) (USD $) In Millions, except Share data, unless otherwise specified | 12 Months Ended | 62 Months Ended |  |  | 1 Months Ended |  | 1 Months Ended |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Dec. 31, 2011 | Dec. 31, 2010 | Dec. 31, 2011 | Aug. 26, 2010 | Nov. 17, 2006 | Feb. 28, 2010 Central National | Feb. 26, 2010 Central National | Dec. 31, 2011 Old Lyme | Dec. 30, 2011 Old Lyme
Business acquisition |  |  |  |  |  |  |  |  |
Cash to be paid on acquisition |  |  |  |  |  |  | $ 5 |  | $ 6
Purchase note acquired |  |  |  |  |  |  |  |  | 2.1
Gain on acquisition |  |  |  |  |  | 12.8 |  | 7.2 |
Share Repurchase |  |  |  |  |  |  |  |  |
Authorized repurchase of common shares (in shares) |  |  |  |  | 1,000,000 |  |  |  |
Additional authorized repurchase of common shares (in shares) |  |  |  | 600,000 |  |  |  |  |
Common shares repurchased and retired during the period (in shares) | 313,967 | 677,125 | 1,411,703 |  |  |  |  |  |
Value of common shares repurchased and retired during the period | $ 114.2 | $ 222.0 | $ 537.5 |  |  |  |  |  |

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