XML 122 R104.htm IDEA: XBRL DOCUMENT
v3.24.0.1

Segment Information - Summary of Premiums Written and Earned by Segment (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | $ 4,274,378 | $ 3,952,482 | $ 3,741,948
Direct premiums written | 4,558,500 | 4,048,500 | 3,907,500
Private passenger automobile |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 2,796,100 | 2,655,700 | 2,613,500
Direct premiums written | 2,841,800 | 2,598,900 | 2,640,700
Homeowners |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 957,700 | 830,600 | 698,100
Direct premiums written | 1,119,000 | 940,300 | 801,500
Commercial automobile |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 303,900 | 267,900 | 258,600
Direct premiums written | 346,200 | 276,800 | 259,900
Other |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 216,700 | 198,300 | 171,700
Direct premiums written | 251,500 | 232,500 | 205,400
Property & Casualty |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 4,245,369 | 3,923,642 | 3,712,910
Direct premiums written | 4,531,942 | 4,018,057 | 3,877,476
Property & Casualty | Private passenger automobile |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 2,796,100 | 2,655,700 | 2,613,500
Direct premiums written | 2,841,800 | 2,598,900 | 2,640,700
Property & Casualty | Homeowners |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 957,700 | 830,600 | 698,100
Direct premiums written | 1,119,000 | 940,300 | 801,500
Property & Casualty | Commercial automobile |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 303,900 | 267,900 | 258,600
Direct premiums written | 346,200 | 276,800 | 259,900
Property & Casualty | Other |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 187,700 | 169,400 | 142,700
Direct premiums written | 224,900 | 202,100 | 175,400
Other |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 29,000 | 28,900 | 29,000
Direct premiums written | 26,600 | 30,400 | 30,000
Other | Private passenger automobile |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 0 | 0 | 0
Direct premiums written | 0 | 0 | 0
Other | Homeowners |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 0 | 0 | 0
Direct premiums written | 0 | 0 | 0
Other | Commercial automobile |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 0 | 0 | 0
Direct premiums written | 0 | 0 | 0
Other | Other |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 29,000 | 28,900 | 29,000
Direct premiums written | $ 26,600 | $ 30,400 | $ 30,000

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 -Topic 944 -SubTopic 605 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (b)(1) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479655/944-605-50-1 + 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 -Topic 944 -SubTopic 235 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Subparagraph (SX 210.12-17(Column E)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480149/944-235-S99-2 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 605 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (c)(3) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479655/944-605-50-1 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04(13)(c)) -SubTopic 220 -Topic 942 -Publisher FASB -URI https://asc.fasb.org//1943274/2147483589/942-220-S99-1 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(1)) -SubTopic 220 -Topic 944 -Publisher FASB -URI https://asc.fasb.org//1943274/2147483586/944-220-S99-1 + 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: |