Name:	dcom_AmortizationOfTransferLoss
Namespace Prefix:	dcom_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

The amortized cost of securities transferred from available-for-sale to held-to-maturity.

No definition available.

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

This item represents the total of all debt securities, at fair value, which are categorized neither as held-to-maturity nor trading securities.

No definition available.

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

The number of TRUPS securities that were deemed to have OTTI as of balance sheet date.

No definition available.

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

The number of trust preferred securities that were transferred from held to maturity to available for sale on September 1, 2008.

No definition available.

Name:	dcom_NumberOfTrustPreferredSecuritiesTransferredFromHeldToMaturityToAvailableForSaleOnSeptember12008
Namespace Prefix:	dcom_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

This item represents reductions in the cumulative amount of credit and non-credit losses recognized in earnings and other comprehensive loss for an other than temporary impairment (OTTI) of a debt security because of the amortization of previously recognized OTTI..

No definition available.

Name:	dcom_OtherThanTemporaryImpairmentCreditAndNonCreditLossesRecognizedInEarningsAndOCIAmortizationOfOTTI
Namespace Prefix:	dcom_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

The cumulative amount of credit and non-credit losses recognized in earnings and other comprehensive loss related to debt securities held for which a portion of an other than temporary impairment (OTTI) was recognized in other comprehensive income (a component of shareholders' equity).

No definition available.

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

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

No definition available.

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

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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

The weighted average term to maturity.

No definition available.

Name:	dcom_SecuritiesWeightedAverageTermToMaturity
Namespace Prefix:	dcom_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

The remaining average life at the time of transfer of the trust preferred securities that were transferred from available for sale to held to maturity.

No definition available.

Name:	dcom_TheRemainingAverageLifeAtTheTimeOfTransferOfTheTrustPreferredSecuritiesThatWereTransferredFromAvailableForSaleToHeldToMaturity
Namespace Prefix:	dcom_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

The net of tax component of accumulated other comprehensive income (loss) related to the unrealized loss on securities transferred.

No definition available.

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

The weighted average duration of all mortgage backed securities available for sale as of the date indicated.

No definition available.

Name:	dcom_WeightedAverageDurationOfMortgageBackedSecuritiesAvailableForSale
Namespace Prefix:	dcom_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

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

This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563

Name:	us-gaap_AvailableForSaleSecuritiesGrossRealizedGains
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

This item represents the gross loss realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

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

The cumulative amount of credit losses recognized in earnings related to debt securities held for which a portion of an other than temporary impairment (OTTI) was recognized in other comprehensive income (a component of shareholders' equity).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27340-111563

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

This item represents reductions in the cumulative amount of credit losses recognized in earnings for an other than temporary impairment (OTTI) of a debt security because of the sale of impaired securities during the period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27340-111563

Name:	us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsReductionsSecuritiesSold
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

No definition available.

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

The cash inflow associated with the sale of equity securities classified as available-for-sale securities.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=49167202&loc=d3e26853-111562

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3179-108585

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Investing Activities
-URI http://asc.fasb.org/extlink&oid=6516133

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

The cash inflow from the sale of securities issued by a governmental agency or corporation (for example, GNMA or FHLMC) or by private issuers (for example, banks and mortgage banking enterprises) secured by and repaid from underlying mortgages, which were designated as available for sale when acquired.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3179-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Investing Activities
-URI http://asc.fasb.org/extlink&oid=6516133

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

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=dcom_PooledTrustPreferredHeldToMaturitySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	dcom_OtherThanTemporaryImpairmentCategoryAxis=dcom_CreditRelatedOttiMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	dcom_OtherThanTemporaryImpairmentCategoryAxis=dcom_NonCreditRelatedOttiMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	dcom_OtherThanTemporaryImpairmentCategoryAxis=dcom_TotalCreditAndNonCreditOttiMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=dcom_AllMortgageBackedSecuritiesAvailableForSaleMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=dcom_MutualFundInvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=dcom_AllInvestmentSecuritiesAvailableForSaleMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=dcom_TransfersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: