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v3.19.1

Segment Information - Summary of Premiums Written and Earned by Segment (Details) - USD ($) $ in Thousands | 3 Months Ended
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Mar. 31, 2019 | Mar. 31, 2018
Segment Reporting Information [Line Items] |  |
Net premiums earned | $ 870,245 | $ 808,084
Direct Premiums Written | 922,100 | 869,000
Private Passenger Automobile Line [Member] |  |
Segment Reporting Information [Line Items] |  |
Net premiums earned | 672,600 | 627,000
Direct Premiums Written | 705,300 | 674,000
Homeowners Line [Member] |  |
Segment Reporting Information [Line Items] |  |
Net premiums earned | 119,300 | 107,800
Direct Premiums Written | 130,900 | 115,300
Commercial Automobile Line [Member] |  |
Segment Reporting Information [Line Items] |  |
Net premiums earned | 49,600 | 44,900
Direct Premiums Written | 54,400 | 49,700
Other [Member] |  |
Segment Reporting Information [Line Items] |  |
Net premiums earned | 28,700 | 28,400
Direct Premiums Written | 31,500 | 30,000
Property and Casualty Lines [Member] |  |
Segment Reporting Information [Line Items] |  |
Net premiums earned | 863,100 | 800,300
Direct Premiums Written | 915,300 | 862,600
Property and Casualty Lines [Member] | Private Passenger Automobile Line [Member] |  |
Segment Reporting Information [Line Items] |  |
Net premiums earned | 672,600 | 627,000
Direct Premiums Written | 705,300 | 674,000
Property and Casualty Lines [Member] | Homeowners Line [Member] |  |
Segment Reporting Information [Line Items] |  |
Net premiums earned | 119,300 | 107,800
Direct Premiums Written | 130,900 | 115,300
Property and Casualty Lines [Member] | Commercial Automobile Line [Member] |  |
Segment Reporting Information [Line Items] |  |
Net premiums earned | 49,600 | 44,900
Direct Premiums Written | 54,400 | 49,700
Property and Casualty Lines [Member] | Other [Member] |  |
Segment Reporting Information [Line Items] |  |
Net premiums earned | 21,600 | 20,600
Direct Premiums Written | 24,700 | 23,600
Other Segments [Member] |  |
Segment Reporting Information [Line Items] |  |
Net premiums earned | 7,100 | 7,800
Direct Premiums Written | 6,800 | 6,400
Other Segments [Member] | Private Passenger Automobile Line [Member] |  |
Segment Reporting Information [Line Items] |  |
Net premiums earned | 0 | 0
Direct Premiums Written | 0 | 0
Other Segments [Member] | Homeowners Line [Member] |  |
Segment Reporting Information [Line Items] |  |
Net premiums earned | 0 | 0
Direct Premiums Written | 0 | 0
Other Segments [Member] | Commercial Automobile Line [Member] |  |
Segment Reporting Information [Line Items] |  |
Net premiums earned | 0 | 0
Direct Premiums Written | 0 | 0
Other Segments [Member] | Other [Member] |  |
Segment Reporting Information [Line Items] |  |
Net premiums earned | 7,100 | 7,800
Direct Premiums Written | $ 6,800 | $ 6,400

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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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- Definition Amount, after premiums ceded to other entities and premiums assumed by the entity, of premiums earned. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(1)) -URI http://asc.fasb.org/extlink&oid=114873790&loc=SL114874131-224263 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 235 -Section S99 -Paragraph 2 -Subparagraph (SX 210.12-17(Column E)) -URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e574992-122915 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04(13)(c)) -URI http://asc.fasb.org/extlink&oid=114873765&loc=SL114874048-224260 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 605 -Section 50 -Paragraph 1 -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547 + Details
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