Reinsurance (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended	12 Months Ended
Jun. 30, 2012	Dec. 31, 2011
Ceded Credit Risk [Line Items]
Excess of loss reinsured under an agreement	$ 1.0
Reinsurance (Textual) [Abstract]
Percentage of share in results of pooled business subsidiary	80.00%
Percentage of share in results of pooled business owned by third party	20.00%
Quota share reinsurance percentage		50.00%
Minimum [Member]
Ceded Credit Risk [Line Items]
Percentage of accumulation of losses	90.00%
Quota share reinsurance reduced percentage	40.00%
Maximum amount of loss coverage under reinsurance agreement of property catastrophe	130.0
Maximum [Member]
Ceded Credit Risk [Line Items]
Percentage of accumulation of losses	100.00%
Quota share reinsurance reduced percentage	50.00%
Maximum amount of loss coverage under reinsurance agreement of property catastrophe	145.0
Catastrophe Reinsurance [Member]
Ceded Credit Risk [Line Items]
Excess of loss reinsured under an agreement	$ 5.0

Maximum amount of loss coverage under reinsurance agreement of property catastrophe.

No definition available.

Name:	dgica_MaximumAmountOfLossCoverageUnderReinsuranceAgreementOfPropertyCatastrophe
Namespace Prefix:	dgica_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Percentage of share in results of pooled business owned by third party.

No definition available.

Name:	dgica_PercentageOfShareInResultsOfPooledBusinessOwnedByThirdParty
Namespace Prefix:	dgica_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Percentage of share in results of pooled business subsidiary.

No definition available.

Name:	dgica_PercentageOfShareInResultsOfPooledBusinessSubsidiary
Namespace Prefix:	dgica_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Quota share reinsurance percentage.

No definition available.

Name:	dgica_QuotaShareReinsurancePercentage
Namespace Prefix:	dgica_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Quota share reinsurance reduced percentage.

No definition available.

Name:	dgica_QuotaShareReinsuranceReducedPercentage
Namespace Prefix:	dgica_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Name:	dgica_ReinsuranceTextualAbstract
Namespace Prefix:	dgica_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Name:	us-gaap_CededCreditRiskLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Ratio of insurance contracts that are subject to reinsurance participation to all contracts in force.

No definition available.

Name:	us-gaap_ContractsInForceSubjectToParticipationThroughReinsurancePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

The value of insurance contracts that are subject to reinsurance participation agreements (risk assumed from other insurers).

No definition available.

Name:	us-gaap_ContractsInForceSubjectToParticipationThroughReinsuranceValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration