EMPLOYEE BENEFIT PLANS, ESOP PLAN and 401k (Details) (USD $) In Thousands, except Share data, unless otherwise specified	0 Months Ended	12 Months Ended
Jun. 26, 1996	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
401 (k) Plan [Abstract]
Discretionary contributions made (benefit expense recognized)		$ 701dcom_PeriodicExpense401kPlan	$ 679dcom_PeriodicExpense401kPlan	$ 647dcom_PeriodicExpense401kPlan
Aggregate amount of participant investments in the Holding Company's common stock		8,827	10,016
ESOP [Member]
Employee Stock Ownership Plan (ESOP) Disclosures [Line Items]
ESOP loan amount	11,638	3,222	3,401
Interest on loan (in hundredths)	8.00%	8.00%	8.00%
Shares Contributed to ESOP	3,927,825
Vesting rate per year of service (in hundredths)	25.00%	25.00%	25.00%
Loan original repayment term, Maximum	10 years	30 years	30 years
ESOP Shares allocated in period		78,155	78,155	78,155
Benefit expense recognized		1,730	1,753	1,691
Dividends paid to ESOP		$ 525	$ 569	$ 613

The interest on the loan as of the balance sheet date.

No definition available.

Name:	dcom_EmployeeStockOwnershipPlanESOPInterestOnLoan
Namespace Prefix:	dcom_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The gross amount of ESOP plan compensation cost recognized during the period which exceeds the amount recognized in the statement of cash flows by adjustments related to dividends and forfeitures.

+ References

No definition available.

+ Details

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

- Definition

The number of share allocated to ESOP participants during the period.

+ References

No definition available.

+ Details

Name:	dcom_EsopSharesAllocatedInPeriod
Namespace Prefix:	dcom_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	dcom_KPlanAbstract
Namespace Prefix:	dcom_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

401 (k) plan investments in the holding company's common stock.

+ References

No definition available.

+ Details

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

- Definition

The maximum loan repayment term.

+ References

No definition available.

+ Details

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

- Definition

The amount of the cost recognized during the period for the 401(K) defined contribution plan.

+ References

No definition available.

+ Details

Name:	dcom_PeriodicExpense401kPlan
Namespace Prefix:	dcom_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount reported as a liability as of the balance sheet date by the entity (the employer) of the loan made by a third-party lender directly to the ESOP.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Direct Loan

-URI http://asc.fasb.org/extlink&oid=6510849

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 40

-Section 25

-Paragraph 9

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6418455&loc=d3e16545-113920

+ Details

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

- Details

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

- Definition

Dividends paid on stock held by an employee stock ownership plan.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 40

-Section 50

-Paragraph 1

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6418621&loc=d3e17540-113929

+ Details

Name:	us-gaap_EmployeeStockOwnershipPlanESOPDividendsPaidToESOP
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Sum of the allocated, committed-to-be-released and suspense shares of the entity held by the plan.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 40

-Section 50

-Paragraph 1

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=6418621&loc=d3e17540-113929

+ Details

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

- Definition

Percentage of vesting of share-based compensation awards.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

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Namespace Prefix:
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Period Type: