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Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Tables) | 12 Months Ended
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Dec. 31, 2020
Accounting Policies [Abstract] |
Summary of Deferred Policy Acquisition Cost Amortization and Net Advertising Expense | The table below presents a summary of deferred policy acquisition cost amortization and net advertising expense:
| Year Ended December 31,
| 2020 |  | 2019 |  | 2018
| (Amounts in millions)
Deferred policy acquisition cost amortization | $ | 627.8 |  |  | $ | 602.1 |  |  | $ | 572.2 |
Net advertising expense | 37.7 |  |  | 42.2 |  |  | 40.9 |
Effects of Reinsurance | The effect of reinsurance on property and casualty premiums written and earned was as follows:
| Year Ended December 31,
| 2020 |  | 2019 |  | 2018
| (Amounts in thousands)
Premiums Written |  |  |  |  |
Direct | $ | 3,624,965 |  |  | $ | 3,742,627 |  |  | $ | 3,524,186 |
Ceded | (50,630) |  |  | (43,785) |  |  | (55,973) |
Assumed | 8,012 |  |  | 919 |  |  | 689 |
Net | $ | 3,582,347 |  |  | $ | 3,699,761 |  |  | $ | 3,468,902 |
Premiums Earned |  |  |  |  |
Direct | $ | 3,574,898 |  |  | $ | 3,626,857 |  |  | $ | 3,386,192 |
Ceded | (56,212) |  |  | (56,725) |  |  | (48,941) |
Assumed | 8,067 |  |  | 910 |  |  | 665 |
Net | $ | 3,526,753 |  |  | $ | 3,571,042 |  |  | $ | 3,337,916 |
Premium Receivable, Allowance for Credit Loss | The following table presents a summary of changes in allowance for credit losses on premiums receivable:
|  | Year Ended December 31,
|  | 2020 |  | 2019 |  | 2018
Beginning balance |  | $ | 1,445 |  |  | $ | 1,458 |  |  | 1,258 |
Cumulative effect of adopting ASU 2016-13 |  | 1,855 |  |  | — |  |  | — |
Beginning balance, as adjusted |  | 3,300 |  |  | 1,458 |  |  | 1,258 |
Provision during the period for expected credit losses |  | 10,294 |  |  | 6,162 |  |  | 6,463 |
Write-off amounts during the period |  | (4,406) |  |  | (7,000) |  |  | (6,908) |
Recoveries during the period of amounts previously written off |  | 812 |  |  | 825 |  |  | 645 |
Ending balance |  | $ | 10,000 |  |  | $ | 1,445 |  |  | $ | 1,458 |
Reinsurance Recoverable, Allowance for Credit Loss | The following table presents a summary of changes in allowance for credit losses on reinsurance recoverables:
|  | Year Ended December 31,
|  | 2020 |  | 2019 |  | 2018
Beginning balance |  | $ | — |  |  | $ | — |  |  | $ | — |
Cumulative effect of adopting ASU 2016-13 |  | 159 |  |  | — |  |  | — |
Beginning balance, as adjusted |  | 159 |  |  | — |  |  | — |
Provision during the period for expected credit losses |  | (68) |  |  | — |  |  | — |
Write-off amounts during the period |  | — |  |  | — |  |  | — |
Recoveries during the period of amounts previously written off |  | — |  |  | — |  |  | — |
Ending balance |  | $ | 91 |  |  | $ | — |  |  | $ | — |

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