Name:	dcom_AllocatedAllowanceBalanceOnTroubledDeebtRestructuredLoanEliminatedDueToImprovementInConditionOfLoan
Namespace Prefix:	dcom_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Amounts allocated within the allowance for loan losses related to troubled debt restructured loans at period end.

No definition available.

Name:	dcom_AllocatedReservesRecognizedForTroubleDebtRestructuringReceivables
Namespace Prefix:	dcom_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Name:	dcom_DelinquentServicedLoansSubjectToFirstLossPositionAbstract
Namespace Prefix:	dcom_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings and are in accrual status.

No definition available.

Name:	dcom_FinancingReceivableModificationRecordedInvestmentInAccrualStatus
Namespace Prefix:	dcom_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings and are in non-accrual status

No definition available.

Name:	dcom_FinancingReceivableModificationRecordedInvestmentInNonAccrualStatus
Namespace Prefix:	dcom_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Number of financing receivables that have been modified by troubled debt restructurings in the period.

No definition available.

Name:	dcom_FinancingReceivableModificationsNumberOfContractsInPeriod
Namespace Prefix:	dcom_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Financing receivables that are less than 90 days past due but more than 30 days past due that have been sold and remain subject to a recourse provision.

No definition available.

Name:	dcom_FinancingReceivableRecordedInvestment30To89DaysPastDue
Namespace Prefix:	dcom_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Number of financing receivables that have been modified by troubled debt restructurings and are in accrual status.

No definition available.

Name:	dcom_FinancingReceivablesModificationAccrualStatusNumberOfContracts
Namespace Prefix:	dcom_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

Number of financing receivables that have been modified by troubled debt restructurings and are in non-accrual status.

No definition available.

Name:	dcom_FinancingReceivablesModificationNonAccrualStatusNumberOfContracts
Namespace Prefix:	dcom_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

Financing receivables that are 90 days or more past due that have been sold and remain subject to a recourse provision.

No definition available.

Name:	dcom_FinancingReceivableSoldToFnmaRecordedInvestmentEqualToGreaterThan90DaysPastDue
Namespace Prefix:	dcom_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Number of financing receivables that are 90 days or more past due that have been sold and remain subject to a recourse provision.

No definition available.

Name:	dcom_NumberOfFinancingReceivablesThatAre90DaysOrMorePastDueThatHaveBeenSoldAndRemainSubjectToRecourseProvision
Namespace Prefix:	dcom_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

Number of financing receivables that are less than 90 days past due but more than 30 days past due that have been sold and remain subject to a recourse provision

No definition available.

Name:	dcom_NumberOfFinancingReceivablesThatAreLessThan90DaysPastDueButMoreThan30DaysPastDueThatHaveBeenSoldAndRemainSubjectToRecourseProvision
Namespace Prefix:	dcom_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

The number of troubled debt restructured loans disposed of in the period that resulted in a charge-off against the allowance for loans losses

No definition available.

Name:	dcom_NumberOfTroubledDebtRestructuredLoansDisposedOfInPeriodWithChargeOffsRecognized
Namespace Prefix:	dcom_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

The number of troubled debt restructured loans for which allocated reserves within the allowance for loan losses were no longer deemed warranted.

No definition available.

Name:	dcom_NumberOsTroubledDebtRestructuredLoansForWhichAllocatedReservesWereNoLongerDeemedWarranted
Namespace Prefix:	dcom_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Name:	dcom_SummaryOfActivityRelatedToTdrsForPeriodAbstract
Namespace Prefix:	dcom_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Name:	dcom_TroubledDebtRestructuringOnReceivablesAbstract
Namespace Prefix:	dcom_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Reflects the amount of loans that have been removed, or charged off, from both trouble debt restructuring loan receivables and the reserve for credit losses, typically because they are considered to be not salvageable or have been purchased by unconsolidated collection entities.

No definition available.

Name:	dcom_TroubleDebtRestructuringAllowanceForLoanAndLeaseLossesWriteOffs
Namespace Prefix:	dcom_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Number of financing receivables that have been modified by troubled debt restructurings.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 33

-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953676-111524

Name:	us-gaap_FinancingReceivableModificationsNumberOfContracts2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Post-modification amount of investment in financing receivables modified by troubled debt restructurings.

Name:	us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Pre-modification amount of investment in financing receivables modified by troubled debt restructurings.

Name:	us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 40

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=25495931&loc=d3e18845-111554

Name:	us-gaap_FinancingReceivableModificationsRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Amount of investment related to financing receivables modified by troubled debt restructurings within the previous 12 months, for which there was a payment default.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 34

-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953682-111524

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Name:	us-gaap_FinancingReceivableTroubledDebtRestructuringAxis=dcom_MixedUseCommercialRealEstateAllowanceMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_FinancingReceivableTroubledDebtRestructuringAxis=dcom_MultifamilyResidentialAndResidentialMixedUseAllowanceMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_FinancingReceivableTroubledDebtRestructuringAxis=dcom_OneToFourFamilyResidentialAndCooperativeUnitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_FinancingReceivableTroubledDebtRestructuringAxis=dcom_TotalRealEstateLoansReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: