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v3.20.2

Subsequent Event (Details) - Subsequent Event [Member] $ in Millions | 1 Months Ended
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Jul. 31, 2020 USD ($)
Subsequent Event [Line Items] |
Premium returns for eligible policyholders, amount, July | $ 22
Reduced premiums earned and written, amount, July | 22
Premium returns for eligible policyholders, amount, total | $ 128

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- Definition Premium Returns for Eligible Policyholders, Amount, July + References No definition available. + Details
Name: | mcy_PremiumReturnsForEligiblePolicyholdersAmountJuly
Namespace Prefix: | mcy_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Premium Returns for Eligible Policyholders, Amount, Total + References No definition available. + Details
Name: | mcy_PremiumReturnsForEligiblePolicyholdersAmountTotal
Namespace Prefix: | mcy_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Reduced premiums earned and written, amount, July + References No definition available. + Details
Name: | mcy_ReducedPremiumsEarnedAndWrittenAmountJuly
Namespace Prefix: | mcy_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event. + References No definition available. + Details
Name: | us-gaap_SubsequentEventLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |