Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953423-111524

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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.

+ References

No definition available.

+ Details

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

- Definition

The balance of financing receivables that were individually evaluated for impairment.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953423-111524

+ Details

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

- Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_CollateralAxis=dcom_CollateralDependentLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

LOANS HELD FOR INVESTMENT, NET - Collateral Dependent Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for impairment		$ 17,069
Individually evaluated for impairment		6,474
Commercial real estate ("CRE")
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for impairment		2,704
Multifamily residential and residential mixed-use
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for impairment		1,863
Commercial and Industrial ("C&I") Loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for impairment		12,502
Individually evaluated for impairment		$ 6,474
Collateral Dependent Loans \| Commercial real estate ("CRE")
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for impairment	$ 53,200
Individually evaluated for impairment	7,600
Collateral Dependent Loans \| Multifamily residential and residential mixed-use
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for impairment	8,500
Individually evaluated for impairment	600
Collateral Dependent Loans \| Commercial and Industrial ("C&I") Loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Individually evaluated for impairment	4,400
Individually evaluated for impairment	$ 700