RESTRICTED STOCK - Narrative (Details) - USD ($)	12 Months Ended
Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Restricted Investments	$ 88,745,000	$ 37,732,000
FHLBNY
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Share price	$ 100
Bank owned shares	636,274	128,184
Decrease in outstanding FHLBNY advances	$ 1,110,000,000
Dividend income on the FHLBNY capital stock	900,000	$ 1,900,000	$ 3,000,000.0
Restricted Investments	$ 63,627,000	$ 12,819,000
FRB capital stock
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Share price	$ 50
Bank owned shares	499,052	494,965
Dividend income on the FHLBNY capital stock	$ 828,000	$ 442,000	0
Restricted Investments	$ 24,953,000	24,748,000
Bankers' Bank capital stock (ACBB)
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Bank owned shares	60
Dividend income on the FHLBNY capital stock	$ 1,000	1,000	$ 0
Restricted Investments	$ 165,000	$ 165,000
Bankers' Bank capital stock (ACBB) \| Minimum
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Share price	$ 2,500
Bankers' Bank capital stock (ACBB) \| Maximum
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Share price	$ 3,250

Amount of increase (decrease) in outstanding FHLBNY advances.

No definition available.

Name:	dcom_IncreaseDecreaseInOutstandingAdvances
Namespace Prefix:	dcom_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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

- Definition

Amount of dividend income on nonoperating securities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.7(a))
-URI https://asc.fasb.org/extlink&oid=126953954&loc=SL114868664-224227

+ Details

Name:	us-gaap_InvestmentIncomeDividend
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Balance held at close of period in number of shares.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 210
-Section 50
-Paragraph 6
-Subparagraph (c)
-URI https://asc.fasb.org/extlink&oid=99383244&loc=d3e12121-115841

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 320
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-12B(Column B))
-URI https://asc.fasb.org/extlink&oid=122147990&loc=d3e611197-123010

+ Details

Name:	us-gaap_InvestmentOwnedBalanceShares
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Investments which are not defined as or included in marketable (debt, equity, or other) securities whose use is restricted in whole or in part, generally by contractual agreements or regulatory requirements. For use in an unclassified balance sheet.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 954
-SubTopic 210
-Section 45
-Paragraph 4
-URI https://asc.fasb.org/extlink&oid=120413173&loc=SL6242262-115580

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 954
-SubTopic 210
-Section 50
-Paragraph 2
-URI https://asc.fasb.org/extlink&oid=127002003&loc=SL6242269-115581

+ Details

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

- Definition

Price of a single share of a number of saleable stocks of a company.

+ References

No definition available.

+ Details

Name:	us-gaap_SharePrice
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	srt_FederalHomeLoanBankAdvancesBranchOfFHLBBankAxis=srt_FederalHomeLoanBankOfNewYorkMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_FederalHomeLoanBankAdvancesBranchOfFHLBBankAxis=dcom_FederalReserveBankMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_FederalHomeLoanBankAdvancesBranchOfFHLBBankAxis=dcom_BankerSBankMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: