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

The amount of loans and leases receivable gross carrying amount, significant payment delay.

No definition available.

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

The amount of loans and leases receivable gross carrying amount, term extension and significant payment delay.

No definition available.

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

Percentage of allowance for credit loss to total financing receivable outstanding.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph (a)
-Subparagraph (1)

Name:	srt_FinancingReceivableAllowanceForCreditLossToOutstandingPercent
Namespace Prefix:	srt_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

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

Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI https://asc.fasb.org/extlink&oid=124259787&loc=d3e4428-111522

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

Name:	us-gaap_LoanRestructuringModificationAxis=us-gaap_PaymentDeferralMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=dcom_OneToFourFamilyResidentialAndCooperativeUnitAllowanceMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=dcom_MultifamilyResidentialAndResidentialMixedUseAllowanceMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialRealEstatePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=dcom_AcquisitionDevelopmentAndConstructionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: