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

Commercial real estate loans more than 90 days past due on principal and interest payments while borrower was finalizing negotiation of new tenant lease.

No definition available.

Name:	dcom_CommercialRealEstateLoanMoreThan90DaysPastDueUnderNegotiationForNewLease
Namespace Prefix:	dcom_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

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

The balance of financing receivables that were individually assigned a credit rating.

No definition available.

Name:	dcom_FinancingReceivableIndividuallyAssignedCreditRating
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 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

The balance of financing receivables that were not individually assigned a credit rating.

No definition available.

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

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

The number of commercial real estate loans more than 90 days past due on principal and interest payments while borrower was finalizing negotiation of new tenant lease.

No definition available.

Name:	dcom_NumberOfCommercialRealEstateLoansMoreThan90DaysPastDueUnderNegotiationForNewLease
Namespace Prefix:	dcom_
Data Type:	xbrli:integerItemType
Balance Type:	na
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

Reflects the net carrying amount of loans and leases held in portfolio secured by real estate, after deducting deferred income, but before deducting the allowance for losses on such loans and leases.

No definition available.

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

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=7512638&loc=SL6953676-111524

Name:	us-gaap_FinancingReceivableModificationsNumberOfContracts1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

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=6951948&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=7512638&loc=SL6953682-111524

Name:	us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
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.

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

Financing receivables that are less than 60 days past due but more than 29 days past due.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 7A

-URI http://asc.fasb.org/extlink&oid=7512638&loc=SL6953401-111524

Name:	us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Financing receivables that are less than 90 days past due but more than 59 days past due.

Name:	us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Recorded investment in financing receivables that are 90 days or more past due and still accruing.

Name:	us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

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

Financing receivables that are current.

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

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

Recorded Investment in financing receivables that are past due at the balance sheet date.

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

Reflects the amount of the write-down related to a troubled debt restructuring.

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

Reflects the carrying amount of loans deemed to be questionable as to collection on which no interest is continuing to be recognized.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 7

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=7512638&loc=d3e5111-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Statement of Position (SOP)

-Number 01-6

-Paragraph 13

-Subparagraph g

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.