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LOANS, Credit Quality Indicator (Details) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
One-to four Family Residential and Cooperative Unit [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Real estate loans not individually assigned a credit rating $ 9,091dcom_FinancingReceivableNotIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_OneToFourFamilyResidentialAndCooperativeUnitAllowanceMember		 [1] $ 11,370dcom_FinancingReceivableNotIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_OneToFourFamilyResidentialAndCooperativeUnitAllowanceMember		 [1]
Financing Receivable, Net 73,500us-gaap_NotesReceivableNet
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_OneToFourFamilyResidentialAndCooperativeUnitAllowanceMember		 73,956us-gaap_NotesReceivableNet
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_OneToFourFamilyResidentialAndCooperativeUnitAllowanceMember
Multifamily Residential and Residential Mixed Use [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Real estate loans not individually assigned a credit rating 0dcom_FinancingReceivableNotIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_MultifamilyResidentialAndResidentialMixedUseAllowanceMember		 [1] 0dcom_FinancingReceivableNotIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_MultifamilyResidentialAndResidentialMixedUseAllowanceMember		 [1]
Financing Receivable, Net 3,298,448us-gaap_NotesReceivableNet
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_MultifamilyResidentialAndResidentialMixedUseAllowanceMember		 2,922,550us-gaap_NotesReceivableNet
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_MultifamilyResidentialAndResidentialMixedUseAllowanceMember
Mixed Use Commercial Real Estate [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Real estate loans not individually assigned a credit rating 0dcom_FinancingReceivableNotIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_MixedUseCommercialRealEstateAllowanceMember		 [1] 0dcom_FinancingReceivableNotIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_MixedUseCommercialRealEstateAllowanceMember		 [1]
Financing Receivable, Net 328,667us-gaap_NotesReceivableNet
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_MixedUseCommercialRealEstateAllowanceMember		 375,910us-gaap_NotesReceivableNet
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_MixedUseCommercialRealEstateAllowanceMember
Commercial Real Estate [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Real estate loans not individually assigned a credit rating 0dcom_FinancingReceivableNotIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember		 [1] 0dcom_FinancingReceivableNotIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember		 [1]
Financing Receivable, Net 416,796us-gaap_NotesReceivableNet
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember		 324,696us-gaap_NotesReceivableNet
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
Construction Loan Receivable [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Real estate loans not individually assigned a credit rating 0dcom_FinancingReceivableNotIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_ConstructionLoanReceivableMember		 [1] 0dcom_FinancingReceivableNotIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_ConstructionLoanReceivableMember		 [1]
Financing Receivable, Net 0us-gaap_NotesReceivableNet
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_ConstructionLoanReceivableMember		 268us-gaap_NotesReceivableNet
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_ConstructionLoanReceivableMember
Total Real Estate Loans [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Real estate loans not individually assigned a credit rating 9,091dcom_FinancingReceivableNotIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_TotalRealEstateAndLoansHeldForSaleReceivableMember		 [1] 11,370dcom_FinancingReceivableNotIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_TotalRealEstateAndLoansHeldForSaleReceivableMember		 [1]
Financing Receivable, Net 4,117,411us-gaap_NotesReceivableNet
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_TotalRealEstateAndLoansHeldForSaleReceivableMember		 3,697,380us-gaap_NotesReceivableNet
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_TotalRealEstateAndLoansHeldForSaleReceivableMember
Consumer Loan [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Financing Receivable, Net 1,829us-gaap_NotesReceivableNet
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerLoanMember		 2,139us-gaap_NotesReceivableNet
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_ConsumerLoanMember
Pass [Member] | One-to four Family Residential and Cooperative Unit [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total real estate loans individually assigned a credit rating 60,764dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_OneToFourFamilyResidentialAndCooperativeUnitAllowanceMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 53,472dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_OneToFourFamilyResidentialAndCooperativeUnitAllowanceMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Pass [Member] | Multifamily Residential and Residential Mixed Use [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total real estate loans individually assigned a credit rating 3,271,430dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_MultifamilyResidentialAndResidentialMixedUseAllowanceMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 2,900,979dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_MultifamilyResidentialAndResidentialMixedUseAllowanceMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Pass [Member] | Mixed Use Commercial Real Estate [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total real estate loans individually assigned a credit rating 317,718dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_MixedUseCommercialRealEstateAllowanceMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 364,808dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_MixedUseCommercialRealEstateAllowanceMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Pass [Member] | Commercial Real Estate [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total real estate loans individually assigned a credit rating 391,227dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 299,122dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Pass [Member] | Construction Loan Receivable [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total real estate loans individually assigned a credit rating 0dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_ConstructionLoanReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 0dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_ConstructionLoanReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Pass [Member] | Total Real Estate Loans [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total real estate loans individually assigned a credit rating 4,041,139dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_TotalRealEstateAndLoansHeldForSaleReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember		 3,618,381dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_TotalRealEstateAndLoansHeldForSaleReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PassMember
Special Mention [Member] | One-to four Family Residential and Cooperative Unit [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total real estate loans individually assigned a credit rating 1,370dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_OneToFourFamilyResidentialAndCooperativeUnitAllowanceMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 6,651dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_OneToFourFamilyResidentialAndCooperativeUnitAllowanceMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Special Mention [Member] | Multifamily Residential and Residential Mixed Use [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total real estate loans individually assigned a credit rating 20,738dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_MultifamilyResidentialAndResidentialMixedUseAllowanceMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 17,938dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_MultifamilyResidentialAndResidentialMixedUseAllowanceMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Special Mention [Member] | Mixed Use Commercial Real Estate [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total real estate loans individually assigned a credit rating 4,944dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_MixedUseCommercialRealEstateAllowanceMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 5,203dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_MixedUseCommercialRealEstateAllowanceMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Special Mention [Member] | Commercial Real Estate [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total real estate loans individually assigned a credit rating 6,431dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 4,420dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Special Mention [Member] | Construction Loan Receivable [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total real estate loans individually assigned a credit rating 0dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_ConstructionLoanReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 0dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_ConstructionLoanReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Special Mention [Member] | Total Real Estate Loans [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total real estate loans individually assigned a credit rating 33,483dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_TotalRealEstateAndLoansHeldForSaleReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember		 34,212dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_TotalRealEstateAndLoansHeldForSaleReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SpecialMentionMember
Substandard [Member] | One-to four Family Residential and Cooperative Unit [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total real estate loans individually assigned a credit rating 2,275dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_OneToFourFamilyResidentialAndCooperativeUnitAllowanceMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 2,463dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_OneToFourFamilyResidentialAndCooperativeUnitAllowanceMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Substandard [Member] | Multifamily Residential and Residential Mixed Use [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total real estate loans individually assigned a credit rating 6,280dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_MultifamilyResidentialAndResidentialMixedUseAllowanceMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 3,633dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_MultifamilyResidentialAndResidentialMixedUseAllowanceMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Substandard [Member] | Mixed Use Commercial Real Estate [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total real estate loans individually assigned a credit rating 6,005dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_MixedUseCommercialRealEstateAllowanceMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 4,579dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_MixedUseCommercialRealEstateAllowanceMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Substandard [Member] | Commercial Real Estate [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total real estate loans individually assigned a credit rating 19,138dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 21,154dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Substandard [Member] | Construction Loan Receivable [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total real estate loans individually assigned a credit rating 0dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_ConstructionLoanReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 268dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_ConstructionLoanReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Substandard [Member] | Total Real Estate Loans [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total real estate loans individually assigned a credit rating 33,698dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_TotalRealEstateAndLoansHeldForSaleReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember		 32,097dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_TotalRealEstateAndLoansHeldForSaleReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_SubstandardMember
Doubtful [Member] | One-to four Family Residential and Cooperative Unit [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total real estate loans individually assigned a credit rating 0dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_OneToFourFamilyResidentialAndCooperativeUnitAllowanceMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_DoubtfulMember		 0dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_OneToFourFamilyResidentialAndCooperativeUnitAllowanceMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_DoubtfulMember
Doubtful [Member] | Multifamily Residential and Residential Mixed Use [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total real estate loans individually assigned a credit rating 0dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_MultifamilyResidentialAndResidentialMixedUseAllowanceMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_DoubtfulMember		 0dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_MultifamilyResidentialAndResidentialMixedUseAllowanceMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_DoubtfulMember
Doubtful [Member] | Mixed Use Commercial Real Estate [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total real estate loans individually assigned a credit rating 0dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_MixedUseCommercialRealEstateAllowanceMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_DoubtfulMember		 1,320dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_MixedUseCommercialRealEstateAllowanceMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_DoubtfulMember
Doubtful [Member] | Commercial Real Estate [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total real estate loans individually assigned a credit rating 0dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_DoubtfulMember		 0dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= us-gaap_CommercialRealEstateMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_DoubtfulMember
Doubtful [Member] | Construction Loan Receivable [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total real estate loans individually assigned a credit rating 0dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_ConstructionLoanReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_DoubtfulMember		 0dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_ConstructionLoanReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_DoubtfulMember
Doubtful [Member] | Total Real Estate Loans [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Total real estate loans individually assigned a credit rating 0dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_TotalRealEstateAndLoansHeldForSaleReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_DoubtfulMember		 1,320dcom_FinancingReceivableIndividuallyAssignedCreditRating
/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis
= dcom_TotalRealEstateAndLoansHeldForSaleReceivableMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_DoubtfulMember
Consumer Loans [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Financing Receivable, Net 1,829us-gaap_NotesReceivableNet
/ dcom_ClassOfFinancingReceivableBySegmentAxis
= us-gaap_ConsumerPortfolioSegmentMember		 2,139us-gaap_NotesReceivableNet
/ dcom_ClassOfFinancingReceivableBySegmentAxis
= us-gaap_ConsumerPortfolioSegmentMember
Consumer Loans [Member] | Performing Financing Receivable [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Financing Receivable, Net 1,825us-gaap_NotesReceivableNet
/ dcom_ClassOfFinancingReceivableBySegmentAxis
= us-gaap_ConsumerPortfolioSegmentMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PerformingFinancingReceivableMember		 2,136us-gaap_NotesReceivableNet
/ dcom_ClassOfFinancingReceivableBySegmentAxis
= us-gaap_ConsumerPortfolioSegmentMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_PerformingFinancingReceivableMember
Consumer Loans [Member] | Non-accrual Financing Receivable [Member]    
Financing Receivable, Recorded Investment [Line Items]    
Financing Receivable, Net $ 4us-gaap_NotesReceivableNet
/ dcom_ClassOfFinancingReceivableBySegmentAxis
= us-gaap_ConsumerPortfolioSegmentMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_NonperformingFinancingReceivableMember		 $ 3us-gaap_NotesReceivableNet
/ dcom_ClassOfFinancingReceivableBySegmentAxis
= us-gaap_ConsumerPortfolioSegmentMember
/ us-gaap_InternalCreditAssessmentAxis
= us-gaap_NonperformingFinancingReceivableMember
[1] Amount comprised of fully performing one- to four-family residential and condominium or cooperative apartment loans with balances equal to or less than the FNMA Limits.