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v3.20.4

Segment Information - Summary of Premiums Written and Earned by Segment (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2020 | Sep. 30, 2020 | Jun. 30, 2020 | Mar. 31, 2020 | Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned | $ 921,860 | $ 899,304 | $ 811,897 | $ 922,574 | $ 925,384 | $ 915,012 | $ 888,776 | $ 870,245 | $ 3,555,635 | $ 3,599,418 | $ 3,368,411
Direct premiums written |  |  |  |  |  |  |  |  | 3,654,200 | 3,774,600 | 3,550,900
Private passenger automobile [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | 2,591,300 | 2,756,500 | 2,602,100
Direct premiums written |  |  |  |  |  |  |  |  | 2,569,000 | 2,820,500 | 2,703,600
Homeowners [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | 601,300 | 514,800 | 459,400
Direct premiums written |  |  |  |  |  |  |  |  | 678,900 | 598,500 | 524,900
Commercial automobile [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | 225,600 | 208,700 | 190,100
Direct premiums written |  |  |  |  |  |  |  |  | 240,800 | 217,300 | 198,500
Other insurance product line [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | 137,400 | 119,400 | 116,800
Direct premiums written |  |  |  |  |  |  |  |  | 165,500 | 138,300 | 123,900
Property and Casualty Lines [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | 3,526,753 | 3,571,042 | 3,337,916
Direct premiums written |  |  |  |  |  |  |  |  | 3,624,965 | 3,742,627 | 3,524,186
Property and Casualty Lines [Member] | Private passenger automobile [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | 2,591,300 | 2,756,500 | 2,602,100
Direct premiums written |  |  |  |  |  |  |  |  | 2,569,000 | 2,820,500 | 2,703,600
Property and Casualty Lines [Member] | Homeowners [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | 601,300 | 514,800 | 459,400
Direct premiums written |  |  |  |  |  |  |  |  | 678,900 | 598,500 | 524,900
Property and Casualty Lines [Member] | Commercial automobile [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | 225,600 | 208,700 | 190,100
Direct premiums written |  |  |  |  |  |  |  |  | 240,800 | 217,300 | 198,500
Property and Casualty Lines [Member] | Other insurance product line [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | 108,600 | 91,000 | 86,300
Direct premiums written |  |  |  |  |  |  |  |  | 136,300 | 106,300 | 97,200
Other Segments [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | 28,800 | 28,400 | 30,500
Direct premiums written |  |  |  |  |  |  |  |  | 29,200 | 32,000 | 26,700
Other Segments [Member] | Private passenger automobile [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | 0 | 0 | 0
Direct premiums written |  |  |  |  |  |  |  |  | 0 | 0 | 0
Other Segments [Member] | Homeowners [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | 0 | 0 | 0
Direct premiums written |  |  |  |  |  |  |  |  | 0 | 0 | 0
Other Segments [Member] | Commercial automobile [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | 0 | 0 | 0
Direct premiums written |  |  |  |  |  |  |  |  | 0 | 0 | 0
Other Segments [Member] | Other insurance product line [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net premiums earned |  |  |  |  |  |  |  |  | 28,800 | 28,400 | 30,500
Direct premiums written |  |  |  |  |  |  |  |  | $ 29,200 | $ 32,000 | $ 26,700

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- Definition Amount, before premiums ceded to other entities and premiums assumed by the entity, of premiums written. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 605 -Section 50 -Paragraph 1 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547 + Details
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