XML 114 R101.htm IDEA: XBRL DOCUMENT
v3.22.4

Segment Information - Summary of Premiums Written and Earned by Segment (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | $ 3,952,482 | $ 3,741,948 | $ 3,555,635
Direct premiums written | 4,048,500 | 3,907,500 | 3,654,200
Private passenger automobile |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 2,655,700 | 2,613,500 | 2,591,300
Direct premiums written | 2,598,900 | 2,640,700 | 2,569,000
Homeowners |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 830,600 | 698,100 | 601,300
Direct premiums written | 940,300 | 801,500 | 678,900
Commercial automobile |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 267,900 | 258,600 | 225,600
Direct premiums written | 276,800 | 259,900 | 240,800
Other |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 198,300 | 171,700 | 137,400
Direct premiums written | 232,500 | 205,400 | 165,500
Property & Casualty |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 3,923,642 | 3,712,910 | 3,526,753
Direct premiums written | 4,018,057 | 3,877,476 | 3,624,965
Property & Casualty | Private passenger automobile |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 2,655,700 | 2,613,500 | 2,591,300
Direct premiums written | 2,598,900 | 2,640,700 | 2,569,000
Property & Casualty | Homeowners |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 830,600 | 698,100 | 601,300
Direct premiums written | 940,300 | 801,500 | 678,900
Property & Casualty | Commercial automobile |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 267,900 | 258,600 | 225,600
Direct premiums written | 276,800 | 259,900 | 240,800
Property & Casualty | Other |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 169,400 | 142,700 | 108,600
Direct premiums written | 202,100 | 175,400 | 136,300
Other |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 28,900 | 29,000 | 28,800
Direct premiums written | 30,400 | 30,000 | 29,200
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 | 28,900 | 29,000 | 28,800
Direct premiums written | $ 30,400 | $ 30,000 | $ 29,200

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: |