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Summary of Significant Accounting Policies - Effects of Reinsurance (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
Premiums Written |  |  |
Direct | $ 4,048,500 | $ 3,907,500 | $ 3,654,200
Net | 3,980,000 | 3,860,000 | 3,610,000
Premiums Earned |  |  |
Direct | 4,022,611 | 3,793,664 | 3,603,780
Ceded | (80,950) | (65,017) | (56,212)
Assumed | 10,821 | 13,301 | 8,067
Net | 3,952,482 | 3,741,948 | 3,555,635
Property & Casualty |  |  |
Premiums Written |  |  |
Direct | 4,018,057 | 3,877,476 | 3,624,965
Ceded | (81,256) | (65,521) | (50,630)
Assumed | 10,743 | 13,361 | 8,012
Net | 3,947,544 | 3,825,316 | 3,582,347
Premiums Earned |  |  |
Direct | 3,993,771 | 3,764,626 | 3,574,898
Ceded | (80,950) | (65,017) | (56,212)
Assumed | 10,821 | 13,301 | 8,067
Net | $ 3,923,642 | $ 3,712,910 | $ 3,526,753

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