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Reinsurance - Additional Information (Detail) | 6 Months Ended
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Jun. 30, 2021 USD ($)
Ceded Credit Risk [Line Items] |
Loss reinsurance, set retention amount for property losses | $ 2,000,000.0
Third Party Reinsurance [Member] |
Ceded Credit Risk [Line Items] |
Percentage of accumulation of losses | 100.00%
Catastrophe reinsurance, set retention amount | $ 15,000,000.0
Maximum amount of loss coverage under reinsurance agreement of property catastrophe | $ 185,000,000.0
Atlantic States [Member] |
Ceded Credit Risk [Line Items] |
Percentage of share in results of pooled business subsidiary | 80.00%
Donegal Mutual [Member] |
Ceded Credit Risk [Line Items] |
Percentage of share in results of pooled business owned by third party | 20.00%
Percentage of accumulation of losses | 100.00%
Catastrophe reinsurance, set retention amount | $ 2,000,000.0
Maximum amount of loss coverage under reinsurance agreement of property catastrophe | 13,000,000.0
Additional coverage amount | $ 5,000,000.0

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- Definition Catastrophe reinsurance agreement contracts retention amount. + References No definition available. + Details
Name: | dgica_CatastropheReinsuranceAgreementContractsRetentionAmount
Namespace Prefix: | dgica_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Loss reinsurance agreement contracts retention amount. + References No definition available. + Details
Name: | dgica_LossReinsuranceAgreementContractsRetentionAmount
Namespace Prefix: | dgica_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Maximum amount of loss coverage under reinsurance agreement of property catastrophe. + References No definition available. + Details
Name: | dgica_MaximumAmountOfLossCoverageUnderReinsuranceAgreementOfPropertyCatastrophe
Namespace Prefix: | dgica_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Percentage of share in results of pooled business owned by third party. + References No definition available. + Details
Name: | dgica_PercentageOfShareInResultsOfPooledBusinessOwnedByThirdParty
Namespace Prefix: | dgica_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Percentage of share in results of pooled business subsidiary. + References No definition available. + Details
Name: | dgica_PercentageOfShareInResultsOfPooledBusinessSubsidiary
Namespace Prefix: | dgica_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- 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_CededCreditRiskLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Ratio of insurance contracts that are subject to reinsurance participation to all contracts in force. + References No definition available. + Details
Name: | us-gaap_ContractsInForceSubjectToParticipationThroughReinsurancePercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of risk reinsured in excess of stated retention per company policy. + References No definition available. + Details
Name: | us-gaap_ReinsuranceRetentionPolicyExcessRetentionAmountReinsured
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Details
Name: | us-gaap_CededCreditRiskAxis=dgica_ThirdPartyReinsuranceMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | dei_LegalEntityAxis=dgica_AtlanticStatesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | dei_LegalEntityAxis=dgica_DonegalMutualMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |