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Insurance Activity - Additional Information (Detail) (USD $) | 3 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | ---
Mar. 31, 2013 | Dec. 31, 2012 | Mar. 19, 2012 | Aug. 31, 2009
Quoted percentage to share base |  |  |  | 50.00%
Balances in the fair market reserve | $ 51,200,000 | $ 52,200,000 |  |
Loss contract fair market reserve | 51,230,000 | 52,217,000 | 63,100,000 |
Decreased value of fair market reserve |  | 10,900,000 |  |
Decrease in expense | $ 1,000,000 |  |  |
WMMRC [Member] |  |  |  |
Second loss layer risk percentage of range minimum |  |  |  | 5.00%
Second loss layer risk percentage of range maximum |  |  |  | 10.00%
First loss layer risk percentage of range minimum |  |  |  | 4.00%
First loss layer risk percentage of range maximum |  |  |  | 5.00%
Minimum period of reinsurance agreements | 5 years |  |  |
Maximum period of reinsurance agreements | 10 years |  |  |

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- Definition Fair Market Value Reserve Balance + References No definition available. + Details
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- Definition Fair Market Value Reserve Decrease + References No definition available. + Details
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- Definition Fair Market Value Reserve Expenses Decrease + References No definition available. + Details
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- Definition First loss layer risk percentage of range maximum. + References No definition available. + Details
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- Definition First loss layer risk percentage of range minimum. + References No definition available. + Details
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- Definition Loss contract fair market value reserve. + References No definition available. + Details
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- Definition Maximum period of reinsurance agreements. + References No definition available. + Details
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- Definition Minimum period of reinsurance agreements. + References No definition available. + Details
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- Definition Quoted percentage to share base. + References No definition available. + Details
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- Definition Second loss layer risk percentage of range maximum. + References No definition available. + Details
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- Definition Second loss layer risk percentage of range minimum. + References No definition available. + Details
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