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Reinsurance (List of Direct, Assumed, and Ceded Reinsurance Amounts) (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Jun. 30, 2020 | Mar. 31, 2020 | Sep. 30, 2021 | Sep. 30, 2020
Premiums written: |  |  |  |  |  |
Change in Direct Premiums Written |  |  |  |  | $ 375,900 |
Change in Direct Premiums Written Percentage |  |  |  |  | 16.00% |
Premiums earned: |  |  |  |  |  |
Net | $ 767,247 | $ 694,541 |  |  | $ 2,232,725 | $ 1,976,915
Loss and loss expenses incurred: |  |  |  |  |  |
Net | $ 505,269 | 447,802 |  |  | 1,340,293 | 1,252,075
COVID-19 [Member] | Commercial & Personal Automobile [Member] | Premium Credit [Member] |  |  |  |  |  |
Premiums written: |  |  |  |  |  |
Direct |  |  | $ 19,700 |  |  |
Return audit and midterm endorsement premium [Member] | COVID-19 [Member] |  |  |  |  |  |
Premiums written: |  |  |  |  |  |
Direct |  |  |  | $ 75,000 |  |
Change in Direct Premiums Written Percentage | 4.00% |  |  |  |  |
Direct Assumed and Ceded Reinsurance Amounts [Member] |  |  |  |  |  |
Premiums written: |  |  |  |  |  |
Direct | $ 932,752 | 839,275 |  |  | 2,796,296 | 2,420,350
Assumed | 7,136 | 5,450 |  |  | 17,541 | 17,902
Ceded | (126,982) | (125,217) |  |  | (369,548) | (346,665)
Net | 812,906 | 719,508 |  |  | 2,444,289 | 2,091,587
Premiums earned: |  |  |  |  |  |
Direct | 877,620 | 803,957 |  |  | 2,568,445 | 2,292,495
Assumed | 6,304 | 6,147 |  |  | 16,391 | 18,375
Ceded | (116,677) | (115,563) |  |  | (352,111) | (333,955)
Net | 767,247 | 694,541 |  |  | 2,232,725 | 1,976,915
Loss and loss expenses incurred: |  |  |  |  |  |
Direct | 655,483 | 530,192 |  |  | 1,557,063 | 1,407,000
Assumed | 4,143 | 4,232 |  |  | 10,807 | 13,430
Ceded | (154,357) | (86,622) |  |  | (227,577) | (168,355)
Net | $ 505,269 | $ 447,802 |  |  | $ 1,340,293 | $ 1,252,075

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