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

The amount of allocated reserves on a loan that entered into a troubled debt restructuring agreement during the period that was eliminated as a result of the borrower paying amounts due under the new agreement.

No definition available.

Name:	dcom_AllocatedReserveOnNewTdrEliminated
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

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

Amount of investment in financing receivables (after modification) modified during the period by troubled debt restructurings.

No definition available.

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

Amount of investment in financing receivables (before modification) modified during the period by troubled debt restructurings.

No definition available.

Name:	dcom_FinancingReceivableModificationsPreModificationRecordedInvestmentInPeriod
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 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

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

The aggregate premium paid on loans purchased during the period to be recognized as an adjustment to the yield on the loans over their respective remaining lives.

No definition available.

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

- References

No definition available.

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

- References

No definition available.

Name:	dcom_TroubledDebtRestructuringOnReceivablesAbstract
Namespace Prefix:	dcom_
Data Type:	xbrli:stringItemType
Balance Type:	na
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=49124121&loc=SL6953676-111524

Name:	us-gaap_FinancingReceivableModificationsNumberOfContracts2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
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.

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

Number of financing receivables that have been modified by troubled debt restructurings within the previous 12 months and 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=49124121&loc=SL6953682-111524

Name:	us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=dcom_OneToFourFamilyResidentialAndCooperativeUnitAllowanceMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

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

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