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Reinsurance (List of Direct, Assumed, and Ceded Reinsurance Amounts) (Details) - USD ($) $ in Thousands | 3 Months Ended
--- | ---
Mar. 31, 2021 | Mar. 31, 2020
Premiums written: |  |
Change in Direct Premiums Written | $ 162,000 |
Change in Direct Premiums Written Percentage | 22.00% |
Premiums earned: |  |
Net | $ 724,960 | $ 651,703
Loss and loss expenses incurred: |  |
Net | $ 413,401 | 400,324
Return audit and midterm endorsement premium [Member] | COVID-19 [Member] |  |
Premiums written: |  |
Direct |  | 75,000
Change in Direct Premiums Written Percentage | 11.00% |
Change in Direct Premiums Written |  |
Premiums written: |  |
Direct | $ 87,000 |
Direct Assumed and Ceded Reinsurance Amounts [Member] |  |
Premiums written: |  |
Direct | 908,774 | 746,431
Assumed | 5,533 | 6,043
Ceded | (116,129) | (105,147)
Net | 798,178 | 647,327
Premiums earned: |  |
Direct | 837,369 | 754,892
Assumed | 5,676 | 6,173
Ceded | (118,085) | (109,362)
Net | 724,960 | 651,703
Loss and loss expenses incurred: |  |
Direct | 441,507 | 425,795
Assumed | 3,447 | 4,898
Ceded | (31,553) | (30,369)
Net | $ 413,401 | $ 400,324

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