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This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Registered Domestic Equity Mutual Funds categorized as Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

No definition available.

Name:	dcom_AvailableForSaleSecuritiesDomesticEquityMutualFundFairValueDisclosure
Namespace Prefix:	dcom_
Data Type:	xbrli:monetaryItemType
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This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Registered Fixed Income Mutual Funds categorized as Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

No definition available.

Name:	dcom_AvailableForSaleSecuritiesFixedIncomeMutualFundFairValueDisclosure
Namespace Prefix:	dcom_
Data Type:	xbrli:monetaryItemType
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This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Registered International Equity Mutual Funds categorized as Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

No definition available.

Name:	dcom_AvailableForSaleSecuritiesInternationalEquityMutualFundFairValueDisclosure
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Data Type:	xbrli:monetaryItemType
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The fair value of collateralized mortgage obligations that have been issued by a Government Sponsored Entity and are measured at fair value on a recurring basis as of the period end.

No definition available.

Name:	dcom_CmosIssuedByGsesMeasuredAtFairValueOnRecurringBasis
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No definition available.

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Data Type:	xbrli:monetaryItemType
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The fair value of pass through certificate mortgage-backed securities that have been issued by a Government Sponsored Entity and are measured at fair value on a recurring basis as of the period end.

No definition available.

Name:	dcom_PassThroughMbsIssuedByGsesMeasuredAtFairValueOnRecurringBasis
Namespace Prefix:	dcom_
Data Type:	xbrli:monetaryItemType
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The fair value of collateralized mortgage obligations that have been issued by a private issuer and are measured at fair value on a recurring basis as of the period end.

No definition available.

Name:	dcom_PrivateIssuerCmosMeasuredAtFairValueOnRecurrignBasis
Namespace Prefix:	dcom_
Data Type:	xbrli:monetaryItemType
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The fair value of pass through certificate mortgage-backed securities that have been issued by a private issuer and are measured at fair value on a recurring basis as of the period end.

No definition available.

Name:	dcom_PrivateIssuerPassThroughMortgageBackedSecuritiesMeasuredAtFairValueOnRecurringBasis
Namespace Prefix:	dcom_
Data Type:	xbrli:monetaryItemType
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No definition available.

Name:	dcom_TradingSecuritiesDomesticEquityMututalFundFairValueDisclosure
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Period Type:	instant

No definition available.

Name:	dcom_TradingSecuritiesFixedIncomeMututalFundFairValueDisclosure
Namespace Prefix:	dcom_
Data Type:	xbrli:monetaryItemType
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Period Type:	instant

No definition available.

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

- Details

Name:	us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
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Carrying amount as of the balance sheet date of land and buildings obtained through foreclosure proceedings or defeasance in full or partial satisfaction of a debt arrangement.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 45

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4437-111522

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 28

-Article 12

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph c

-Subparagraph Schedule III

-Article 5