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

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

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

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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.

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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
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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.

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Namespace Prefix:	dcom_
Data Type:	xbrli:monetaryItemType
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Number of financing receivables that have been modified by troubled debt restructurings in the period.

No definition available.

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Data Type:	xbrli:integerItemType
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Amount of investment in financing receivables (after modification) modified during the period by troubled debt restructurings.

No definition available.

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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
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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.

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

No definition available.

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Namespace Prefix:	dcom_
Data Type:	xbrli:integerItemType
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Financing receivables that are 90 days or more past due that have been sold and remain subject to a recourse provision.

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Loans receivables that are 90 days or more past due and still accruing and have not been satisfied or pending refinancing as of the balance sheet date.

No definition available.

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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.

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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.

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

Number of loans receivables that are 90 days or more past due and still accruing and have not been satisfied or pending refinancing as of the balance sheet date.

No definition available.

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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.

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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

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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
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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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

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Data Type:	xbrli:integerItemType
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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

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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

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

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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Period Type:	instant

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

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

Financing receivables that are current.

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Namespace Prefix:	us-gaap_
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Balance Type:	debit
Period Type:	instant

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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 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.

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Data Type:	xbrli:monetaryItemType
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Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

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

-Publisher OTS

-Name Federal Regulation (FR)

-Number Title 12

-Section 563c.102

-Paragraph 8

-Subparagraph e

-Chapter V

-Subsection I

-LegacyDoc This is a non-GAAP reference that was included in the 2009 taxonomy. It will be removed from future versions of this taxonomy.

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

-Publisher AICPA

-Name Audit and Accounting Guide (AAG)

-Number AAG-DEP

-Paragraph 116

-IssueDate 2006-05-01

-Chapter 8

-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.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=7512638&loc=d3e5074-111524

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6375948&loc=d3e4428-111522

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Statement of Position (SOP)

-Number 01-6

-Paragraph 13

-Subparagraph e

-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.