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Segment Reporting Disclosures (Summary of Gross Premium Volume and Net Written Premiums) (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Schedule of GWP and NWP, by Segment [Line Items] |  |  |
Gross written premiums | $ 14,002,237 | $ 13,201,682 | $ 11,438,682
Net written premiums | 8,397,575 | 8,203,390 | 7,119,731
Underwriting Operations [Member] |  |  |
Schedule of GWP and NWP, by Segment [Line Items] |  |  |
Gross written premiums | 10,277,632 | 9,847,538 | 8,485,929
Net written premiums | 8,398,788 | 8,207,373 | 7,125,166
Insurance [Member] |  |  |
Schedule of GWP and NWP, by Segment [Line Items] |  |  |
Gross written premiums | 9,217,150 | 8,606,700 | 7,239,676
Net written premiums | 7,432,062 | 7,040,176 | 5,998,890
Reinsurance [Member] |  |  |
Schedule of GWP and NWP, by Segment [Line Items] |  |  |
Gross written premiums | 1,046,539 | 1,229,851 | 1,246,143
Net written premiums | 967,799 | 1,167,312 | 1,126,167
Other underwriting [Member] |  |  |
Schedule of GWP and NWP, by Segment [Line Items] |  |  |
Gross written premiums | 13,943 | 10,987 | 110
Net written premiums | (1,073) | (115) | 109
Program services and other fronting [Member] |  |  |
Schedule of GWP and NWP, by Segment [Line Items] |  |  |
Gross written premiums | 3,724,605 | 3,354,144 | 2,952,753
Net written premiums | $ (1,213) | $ (3,983) | $ (5,435)

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