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Reinsurance (List of Direct, Assumed, and Ceded Reinsurance Amounts) (Details) (USD $) | 3 Months Ended
--- | ---
Mar. 31, 2012 | Mar. 31, 2011
Premiums written: |  |
Direct | $ 475,966,000 | $ 423,342,000
Assumed | 21,989,000 | 5,653,000
Ceded premiums written | (77,783,000) | (67,160,000)
Net | 420,172,000 | 361,835,000
Premiums earned: |  |
Direct | 451,988,000 | 412,879,000
Assumed | 15,049,000 | 5,889,000
Ceded premiums earned | (88,208,000) | (67,425,000)
Net | 378,829,000 | 351,343,000
Losses and loss expenses incurred: |  |
Direct | 252,203,000 | 269,404,000
Assumed | 10,599,000 | 3,833,000
Ceded losses and loss expenses incurred | (9,896,000) | (24,031,000)
Net | 252,906,000 | 249,206,000
Increase in direct premiums written | 52,600,000 |
Average of Personal Lines filed rate increases that were effective during the period | 5.90% |
Increase in assumed premiums written | 16,300,000 |
Increase in assumed written premiums earned | 9,200,000 |
Excess And Surplus Operations [Member] |  |
Losses and loss expenses incurred: |  |
Increase in direct premiums written | 13,200,000 |
Total Commercial Lines [Member] |  |
Losses and loss expenses incurred: |  |
Renewal pure price | 5.10% |
Increase in retention | 3 |
Retention | 83.00% |
Total Personal Lines [Member] |  |
Losses and loss expenses incurred: |  |
Increase in retention | 1 |
Retention | 87.00% |
New Business [Member] |  |
Losses and loss expenses incurred: |  |
Increase in direct premiums written | 21,800,000 |
Audit And Endorsement Additional Return Premium [Member] |  |
Premiums written: |  |
Direct | $ 5,700,000 | $ (4,000,000)

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