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COMMITMENTS AND CONTINGENCIES AND OTHER MATTERS - Narrative (Details) - BNB Bank (Bank) $ in Millions | Dec. 31, 2020 USD ($)
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Commitments and Contingencies [Line Items] |
Average balance maintained | $ 342.4
Lines of credit with unaffiliated correspondent banks to provide short-term credit | 418.0
Amount available for transactions under Master Repurchase Agreement | 1,900.0
Federal Home Loan Bank Advances |
Commitments and Contingencies [Line Items] |
Lines of credit available on an unsecured basis | 398.0
Federal funds purchased | $ 0.0

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- Definition Represents the amount available for transactions under Master Repurchase agreement with FHLB whereby FHLB agrees to purchase securities from the entity upon the entity's request, with the simultaneous agreement to sell the same or similar securities back to the entity at a future date. + References No definition available. + Details
Name: | dcom_AmountAvailableForTransactionsUnderMasterRepurchaseAgreementWithFHLB
Namespace Prefix: | dcom_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Represents amount of average balance invested with Federal Reserve Bank. + References No definition available. + Details
Name: | dcom_AverageBalancesInvestedWithFederalReserveBank
Namespace Prefix: | dcom_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- References No definition available. + Details
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Namespace Prefix: | dcom_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility on an unsecured basis. + References No definition available. + Details
Name: | dcom_LineOfCreditFacilityMaximumBorrowingCapacityUnsecured
Namespace Prefix: | dcom_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Amount of short term borrowing where a bank borrows, at the federal funds rate, from another bank. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.13(1)) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |