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Summary of Significant Accounting Policies - Effects of Reinsurance (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Premiums Written |  |  |
Direct | $ 3,907,500 | $ 3,654,200 | $ 3,774,600
Net | 3,860,000 | 3,610,000 | 3,730,000
Premiums Earned |  |  |
Direct | 3,793,664 | 3,603,780 | 3,655,233
Ceded | (65,017) | (56,212) | (56,725)
Assumed | 13,301 | 8,067 | 910
Net | 3,741,948 | 3,555,635 | 3,599,418
Property & Casualty |  |  |
Premiums Written |  |  |
Direct | 3,877,476 | 3,624,965 | 3,742,627
Ceded | (65,521) | (50,630) | (43,785)
Assumed | 13,361 | 8,012 | 919
Net | 3,825,316 | 3,582,347 | 3,699,761
Premiums Earned |  |  |
Direct | 3,764,626 | 3,574,898 | 3,626,857
Ceded | (65,017) | (56,212) | (56,725)
Assumed | 13,301 | 8,067 | 910
Net | $ 3,712,910 | $ 3,526,753 | $ 3,571,042

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