XML 66 R54.htm IDEA: XBRL DOCUMENT
v3.22.2.2

Segment Information - Summary of Premiums Written and Earned by Segment (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2022 | Sep. 30, 2021 | Sep. 30, 2022 | Sep. 30, 2021
Segment Reporting Information [Line Items] |  |  |  |
Net premiums earned | $ 996,939 | $ 940,941 | $ 2,947,000 | $ 2,783,682
Direct premiums written | 1,057,100 | 1,032,100 | 3,109,500 | 2,958,400
Private passenger automobile |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Net premiums earned | 665,600 | 652,000 | 1,990,900 | 1,956,600
Direct premiums written | 680,600 | 693,900 | 2,015,600 | 2,006,400
Homeowners |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Net premiums earned | 213,000 | 178,900 | 610,900 | 509,100
Direct premiums written | 251,800 | 222,600 | 713,900 | 600,700
Commercial automobile |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Net premiums earned | 68,000 | 65,600 | 198,600 | 192,800
Direct premiums written | 66,500 | 62,300 | 207,900 | 197,400
Other |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Net premiums earned | 50,300 | 44,400 | 146,600 | 125,200
Direct premiums written | 58,200 | 53,300 | 172,100 | 153,900
Property & Casualty |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Net premiums earned | 989,688 | 933,605 | 2,925,410 | 2,761,934
Direct premiums written | 1,049,088 | 1,024,753 | 3,086,222 | 2,934,777
Property & Casualty | Private passenger automobile |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Net premiums earned | 665,600 | 652,000 | 1,990,900 | 1,956,600
Direct premiums written | 680,600 | 693,900 | 2,015,600 | 2,006,400
Property & Casualty | Homeowners |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Net premiums earned | 213,000 | 178,900 | 610,900 | 509,100
Direct premiums written | 251,800 | 222,600 | 713,900 | 600,700
Property & Casualty | Commercial automobile |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Net premiums earned | 68,000 | 65,600 | 198,600 | 192,800
Direct premiums written | 66,500 | 62,300 | 207,900 | 197,400
Property & Casualty | Other |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Net premiums earned | 43,100 | 37,100 | 125,000 | 103,400
Direct premiums written | 50,200 | 46,000 | 148,800 | 130,300
Other |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Net premiums earned | 7,200 | 7,300 | 21,600 | 21,800
Direct premiums written | 8,000 | 7,300 | 23,300 | 23,600
Other | Private passenger automobile |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Net premiums earned | 0 | 0 | 0 | 0
Direct premiums written | 0 | 0 | 0 | 0
Other | Homeowners |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Net premiums earned | 0 | 0 | 0 | 0
Direct premiums written | 0 | 0 | 0 | 0
Other | Commercial automobile |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Net premiums earned | 0 | 0 | 0 | 0
Direct premiums written | 0 | 0 | 0 | 0
Other | Other |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Net premiums earned | 7,200 | 7,300 | 21,600 | 21,800
Direct premiums written | $ 8,000 | $ 7,300 | $ 23,300 | $ 23,600

X
- 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 https://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547 + Details
Name: | us-gaap_DirectPremiumsWritten
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- 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 https://asc.fasb.org/extlink&oid=120400993&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 https://asc.fasb.org/extlink&oid=120401096&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 https://asc.fasb.org/extlink&oid=120399700&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 https://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547 + Details
Name: | us-gaap_PremiumsEarnedNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_SegmentReportingInformationLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | srt_ProductOrServiceAxis=us-gaap_PropertyAndCasualtyPersonalInsuranceProductLineMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ProductOrServiceAxis=us-gaap_PropertyInsuranceProductLineMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ProductOrServiceAxis=us-gaap_PropertyAndCasualtyCommercialInsuranceProductLineMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ProductOrServiceAxis=us-gaap_OtherInsuranceProductLineMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=mcy_PropertyandCasualtyLinesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=us-gaap_AllOtherSegmentsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |