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

No definition available.

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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.

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Period Type:	instant

Amount of available-for-sale debt securities at cost, net of adjustments, maturing in the next fiscal year through the third fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings (less any cumulative-effect adjustments, as defined) and fair value hedge accounting adjustments.

No definition available.

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Amount of available-for-sale debt securities at fair value maturing in the first fiscal year through the third fiscal year following the latest fiscal year.

No definition available.

Name:	dcom_DueAfterOneYearThroughThreeYearsFairValue
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Amount of available-for-sale debt securities at cost, net of adjustments, maturing in the third fiscal year through the fifth fiscal year following the latest fiscal year. Adjustments include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings (less any cumulative-effect adjustments, as defined) and fair value hedge accounting adjustments.

No definition available.

Name:	dcom_DueAfterThreeYearsThroughFiveYears
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Amount of available-for-sale debt securities at fair value maturing in the third fiscal year through the fifth fiscal year following the latest fiscal year.

No definition available.

Name:	dcom_DueAfterThreeYearsThroughFiveYearsFairValue
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Data Type:	xbrli:monetaryItemType
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The gross gains recognized on the sales of mortgage backed securities during the period.

No definition available.

Name:	dcom_GainOnThesaleOfMortgageBackedSecurities
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Data Type:	xbrli:monetaryItemType
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The number of TRUPS securities that were deemed to have OTTI as of balance sheet date.

No definition available.

Name:	dcom_HeldToMaturitySecuritiesWithOttiNumberOfSecurities
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This item represents an increase to 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 held for which a previous OTTI was recognized and the investor does not intend to sell the debt security and it is not more likely than not that the investor will be required to sell the debt security before recovery of its amortized cost basis.

No definition available.

Name:	dcom_OtherThanTemporaryImpairmentCreditAndNonCreditLossesRecognizedInEarningsAndOCIAdditionsAdditionalLosses
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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.

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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.

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The weighted average term to maturity.

No definition available.

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

No definition available.

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Data Type:	xbrli:monetaryItemType
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The weighted average duration of all mortgage backed securities available for sale as of the date indicated.

No definition available.

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Amount of available-for-sale debt securities at cost, net of adjustments, which include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings (less any cumulative-effect adjustments, as defined) and fair value hedge accounting adjustments.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.2)

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-Topic 320

-SubTopic 10

-Section 50

-Paragraph 2

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The difference between the carrying value and the sale price of debt securities, not separately or otherwise categorized as trading, available-for-sale, or held-to-maturity. This element refers to the gain (loss) included in earnings and not to the cash proceeds of the sale.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

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-Topic 942

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-Section S99

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-Subparagraph (SX 210.9-04.13(h))

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-Topic 944

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-04.3(a))

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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

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Name:	us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsCreditLossesOnDebtSecuritiesHeld
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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

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Name:	us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsReductionsSecuritiesSold
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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

-Glossary Investing Activities

-URI http://asc.fasb.org/extlink&oid=6516133

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

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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.