XML 65 R71.htm IDEA: XBRL DOCUMENT v2.4.1.9
EMPLOYEE BENEFIT PLANS (Details) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]      
Eligibility age, Minimum 21 years    
Eligibility service period, Minimum 1 year    
Age of eligibility for outside director under Director Retirement Plan 75 years    
Employee Retirement Plan [Member]      
Net Periodic Benefit Cost [Abstract]      
Service Cost $ 0us-gaap_DefinedBenefitPlanServiceCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
$ 0us-gaap_DefinedBenefitPlanServiceCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
$ 0us-gaap_DefinedBenefitPlanServiceCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
Interest Cost 1,003us-gaap_DefinedBenefitPlanInterestCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
877us-gaap_DefinedBenefitPlanInterestCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
921us-gaap_DefinedBenefitPlanInterestCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
Expected return on plan assets (1,774)us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
(1,518)us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
(1,451)us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
Amortization of unrealized loss 948us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
1,803us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
1,792us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
Net periodic cost 177us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
1,162us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
1,262us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
Reconciliation of Projected benefit obligation [Roll Forward]      
Accumulated benefit obligation at end of period 27,635us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
22,751us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
 
Projected benefit obligation at beginning of period 22,751us-gaap_DefinedBenefitPlanBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
24,640us-gaap_DefinedBenefitPlanBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
 
Actuarial adjustment 0us-gaap_DefinedBenefitPlanPlanAmendments
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
0us-gaap_DefinedBenefitPlanPlanAmendments
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
 
Service Cost 0us-gaap_DefinedBenefitPlanServiceCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
0us-gaap_DefinedBenefitPlanServiceCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
0us-gaap_DefinedBenefitPlanServiceCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
Interest Cost 1,003us-gaap_DefinedBenefitPlanInterestCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
877us-gaap_DefinedBenefitPlanInterestCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
921us-gaap_DefinedBenefitPlanInterestCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
Actuarial Loss 5,166us-gaap_DefinedBenefitPlanActuarialGainLoss
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
(1,541)us-gaap_DefinedBenefitPlanActuarialGainLoss
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
 
Benefit payments (1,183)us-gaap_DefinedBenefitPlanBenefitsPaid
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
(1,099)us-gaap_DefinedBenefitPlanBenefitsPaid
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
 
Settlements (102)us-gaap_DefinedBenefitPlanSettlementsBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
(126)us-gaap_DefinedBenefitPlanSettlementsBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
 
Projected benefit obligation at end of period 27,635us-gaap_DefinedBenefitPlanBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
22,751us-gaap_DefinedBenefitPlanBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
24,640us-gaap_DefinedBenefitPlanBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
Plan assets at fair value [Roll Forward]      
Balance at beginning of period 24,402us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
20,958us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
 
Return on plan assets 1,327us-gaap_DefinedBenefitPlanActualReturnOnPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
4,156us-gaap_DefinedBenefitPlanActualReturnOnPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
 
Contributions 13us-gaap_DefinedBenefitPlanContributionsByEmployer
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
513us-gaap_DefinedBenefitPlanContributionsByEmployer
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
 
Benefit payments (1,183)us-gaap_DefinedBenefitPlanBenefitsPaid
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
(1,099)us-gaap_DefinedBenefitPlanBenefitsPaid
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
 
Settlements (102)us-gaap_DefinedBenefitPlanPurchasesSalesAndSettlements
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
(126)us-gaap_DefinedBenefitPlanPurchasesSalesAndSettlements
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
 
Balance at end of period 24,457us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
24,402us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
20,958us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
Funded Status [Abstract]      
Deficiency of plan assets over projected benefit obligation (3,178)us-gaap_DefinedBenefitPlanPlansWithBenefitObligationsInExcessOfPlanAssetsAggregateBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
1,651us-gaap_DefinedBenefitPlanPlansWithBenefitObligationsInExcessOfPlanAssetsAggregateBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
 
Accrued retirement expense included in other liabilities (3,178)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
1,651us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
 
Change in accumulated other comprehensive income (loss) [Abstract]      
Balance at beginning of period (8,798)us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
(14,780)us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
 
Adjustment for change in actuarial calculation   0us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
 
Amortization of unrealized loss 948us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
1,803us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
1,792us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
Loss recognized during the year (5,613)us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
4,179us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
 
Balance at the end of the period (13,463)us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
(8,798)us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
(14,780)us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
Period end component of accumulated other comprehensive loss (net of tax) 7,384us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeMinimumPensionLiabilityAfterTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
4,826us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeMinimumPensionLiabilityAfterTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
 
Employer contributions in next fiscal year 14us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInNextFiscalYear
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
   
Actuarial losses anticipated to be recognized as component of net periodic cost 1,677us-gaap_DefinedBenefitPlanAmountToBeAmortizedFromAccumulatedOtherComprehensiveIncomeLossNextFiscalYear
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
   
Assumptions Used in Calculations [Abstract]      
Discount rate used for net periodic cost (credit) (in hundredths) 4.56%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
3.67%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
4.15%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
Discount rate used to determine benefit obligation at period end (in hundredths) 3.72%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
4.56%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
3.67%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
Expected long-term return on plan assets used for net periodic cost (credit) (in hundredths) 7.50%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
7.50%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
7.50%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
Expected long-term return on plan assets used to determine benefit obligation at period end (in hundredths) 7.00%dcom_ExpectedLongTermReturnOnPlanAssetsUsedToDetermineBenefitObligationAtPeriodEnd
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
7.50%dcom_ExpectedLongTermReturnOnPlanAssetsUsedToDetermineBenefitObligationAtPeriodEnd
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
7.50%dcom_ExpectedLongTermReturnOnPlanAssetsUsedToDetermineBenefitObligationAtPeriodEnd
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
Weighted average allocation by asset category of the assets [Abstract]      
Target plan asset allocations (in hundredth) 100.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
100.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
 
Expected rate of return (in hundredths) 7.00%dcom_ExpectedRateOfReturn
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
   
Long-term inflation rate (in hundredths) 2.50%dcom_LongTermInflationRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
   
Expected Future Benefit Payments [Abstract]      
2015 1,616us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
   
2016 1,639us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
   
2017 1,625us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
   
2018 1,616us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
   
2019 1,613us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
   
2020 to 2024 7,858us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
   
Employee Retirement Plan [Member] | Fair Value [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 24,457us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
24,402us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
 
Employee Retirement Plan [Member] | Equity Securities [Member]      
Weighted average allocation by asset category of the assets [Abstract]      
Target plan asset allocations (in hundredth) 66.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_EquitySecuritiesMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
71.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_EquitySecuritiesMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
 
Employee Retirement Plan [Member] | Equity Securities [Member] | Minimum [Member]      
Weighted average allocation by asset category of the assets [Abstract]      
Expected rate of return (in hundredths) 6.00%dcom_ExpectedRateOfReturn
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_EquitySecuritiesMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
   
Employee Retirement Plan [Member] | Equity Securities [Member] | Maximum [Member]      
Weighted average allocation by asset category of the assets [Abstract]      
Expected rate of return (in hundredths) 8.00%dcom_ExpectedRateOfReturn
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_EquitySecuritiesMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
   
Employee Retirement Plan [Member] | Debt Securities [Member]      
Weighted average allocation by asset category of the assets [Abstract]      
Target plan asset allocations (in hundredth) 32.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_DebtSecuritiesMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
29.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_DebtSecuritiesMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
 
Employee Retirement Plan [Member] | Domestic Large Cap, Mutual Fund [Member] | Fair Value [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 2,920us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_DomesticLargeCapMutualFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
6,621us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_DomesticLargeCapMutualFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
 
Employee Retirement Plan [Member] | Domestic Large Cap, Mutual Fund [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 2,920us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_DomesticLargeCapMutualFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
6,621us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_DomesticLargeCapMutualFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
 
Employee Retirement Plan [Member] | Domestic Large Cap, Mutual Fund [Member] | Significant Other Observable Inputs (Level 2) [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_DomesticLargeCapMutualFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_DomesticLargeCapMutualFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
 
Employee Retirement Plan [Member] | Domestic Large Cap, Mutual Fund [Member] | Significant Unobservable Inputs (Level 3) [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_DomesticLargeCapMutualFundMember
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0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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= dcom_EmployeeRetirementPlanMember
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= us-gaap_FairValueInputsLevel3Member
 
Employee Retirement Plan [Member] | Domestic Mid Cap Equity Mutual Fund [Member] | Fair Value [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 1,417us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_DomesticMidCapEquityMutualFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Employee Retirement Plan [Member] | Domestic Mid Cap Equity Mutual Fund [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 1,417us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_DomesticMidCapEquityMutualFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
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Employee Retirement Plan [Member] | Domestic Mid Cap Equity Mutual Fund [Member] | Significant Other Observable Inputs (Level 2) [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_DomesticMidCapEquityMutualFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
   
Employee Retirement Plan [Member] | Domestic Mid Cap Equity Mutual Fund [Member] | Significant Unobservable Inputs (Level 3) [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_DomesticMidCapEquityMutualFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
   
Employee Retirement Plan [Member] | Domestic Small Cap, Mutual Fund [Member] | Fair Value [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 499us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_DomesticSmallCapMutualFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
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/ us-gaap_FairValueByFairValueHierarchyLevelAxis
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3,455us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
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= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
 
Employee Retirement Plan [Member] | Domestic Small Cap, Mutual Fund [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 499us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_DomesticSmallCapMutualFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
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3,455us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
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= dcom_EmployeeRetirementPlanMember
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= us-gaap_FairValueInputsLevel1Member
 
Employee Retirement Plan [Member] | Domestic Small Cap, Mutual Fund [Member] | Significant Other Observable Inputs (Level 2) [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_DomesticSmallCapMutualFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
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0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
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= dcom_EmployeeRetirementPlanMember
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Employee Retirement Plan [Member] | Domestic Small Cap, Mutual Fund [Member] | Significant Unobservable Inputs (Level 3) [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_DomesticSmallCapMutualFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
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0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
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/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
 
Employee Retirement Plan [Member] | International Equity Mutual Fund [Member] | Fair Value [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 3,076us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_InternationalEquityMutualFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
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/ us-gaap_FairValueByFairValueHierarchyLevelAxis
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2,790us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
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/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
 
Employee Retirement Plan [Member] | International Equity Mutual Fund [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 3,076us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_InternationalEquityMutualFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
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2,790us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_InternationalEquityMutualFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
 
Employee Retirement Plan [Member] | International Equity Mutual Fund [Member] | Significant Other Observable Inputs (Level 2) [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_InternationalEquityMutualFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
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/ us-gaap_FairValueByFairValueHierarchyLevelAxis
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0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
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= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
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Employee Retirement Plan [Member] | International Equity Mutual Fund [Member] | Significant Unobservable Inputs (Level 3) [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_InternationalEquityMutualFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
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0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_InternationalEquityMutualFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
 
Employee Retirement Plan [Member] | Fixed Income, Mutual Fund [Member] | Fair Value [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 7,786us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_FixedIncomeMututalFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
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4,747us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
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= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
 
Employee Retirement Plan [Member] | Fixed Income, Mutual Fund [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 7,786us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_FixedIncomeMututalFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
4,747us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
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= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
 
Employee Retirement Plan [Member] | Fixed Income, Mutual Fund [Member] | Significant Other Observable Inputs (Level 2) [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_FixedIncomeMututalFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
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0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
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= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
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Employee Retirement Plan [Member] | Fixed Income, Mutual Fund [Member] | Significant Unobservable Inputs (Level 3) [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_FixedIncomeMututalFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
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0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
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/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
 
Employee Retirement Plan [Member] | Fixed Income [Member] | Minimum [Member]      
Weighted average allocation by asset category of the assets [Abstract]      
Expected rate of return (in hundredths) 3.00%dcom_ExpectedRateOfReturn
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_FixedIncomeFundsMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
   
Employee Retirement Plan [Member] | Fixed Income [Member] | Maximum [Member]      
Weighted average allocation by asset category of the assets [Abstract]      
Expected rate of return (in hundredths) 5.00%dcom_ExpectedRateOfReturn
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_FixedIncomeFundsMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
   
Employee Retirement Plan [Member] | Cash Equivalent Mutual Fund [Member]      
Weighted average allocation by asset category of the assets [Abstract]      
Target plan asset allocations (in hundredth) 2.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_CashEquivalentMutualFundMember
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= dcom_EmployeeRetirementPlanMember
0.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_CashEquivalentMutualFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
 
Employee Retirement Plan [Member] | Cash Equivalent Mutual Fund [Member] | Fair Value [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 687us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_CashEquivalentMutualFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Employee Retirement Plan [Member] | Cash Equivalent Mutual Fund [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 687us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_CashEquivalentMutualFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
   
Employee Retirement Plan [Member] | Cash Equivalent Mutual Fund [Member] | Significant Other Observable Inputs (Level 2) [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_CashEquivalentMutualFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
   
Employee Retirement Plan [Member] | Cash Equivalent Mutual Fund [Member] | Significant Unobservable Inputs (Level 3) [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_CashEquivalentMutualFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
   
Employee Retirement Plan [Member] | Domestic Large Cap, Common Collective Investment Funds [Member] | Fair Value [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 5,012us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_DomesticLargeCapCommonCollectiveInvestmentFundsMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
4,435us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_DomesticLargeCapCommonCollectiveInvestmentFundsMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
 
Employee Retirement Plan [Member] | Domestic Large Cap, Common Collective Investment Funds [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_DomesticLargeCapCommonCollectiveInvestmentFundsMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_DomesticLargeCapCommonCollectiveInvestmentFundsMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
 
Employee Retirement Plan [Member] | Domestic Large Cap, Common Collective Investment Funds [Member] | Significant Other Observable Inputs (Level 2) [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 5,012us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_DomesticLargeCapCommonCollectiveInvestmentFundsMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
4,435us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_DomesticLargeCapCommonCollectiveInvestmentFundsMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
 
Employee Retirement Plan [Member] | Domestic Large Cap, Common Collective Investment Funds [Member] | Significant Unobservable Inputs (Level 3) [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_DomesticLargeCapCommonCollectiveInvestmentFundsMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_DomesticLargeCapCommonCollectiveInvestmentFundsMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
 
Employee Retirement Plan [Member] | Domestic Mid Cap Common Collective Trust Fund [Member] | Fair Value [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 679us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_DomesticMidCapCommonCollectiveTrustFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Employee Retirement Plan [Member] | Domestic Mid Cap Common Collective Trust Fund [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_DomesticMidCapCommonCollectiveTrustFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
   
Employee Retirement Plan [Member] | Domestic Mid Cap Common Collective Trust Fund [Member] | Significant Other Observable Inputs (Level 2) [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 679us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_DomesticMidCapCommonCollectiveTrustFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
   
Employee Retirement Plan [Member] | Domestic Mid Cap Common Collective Trust Fund [Member] | Significant Unobservable Inputs (Level 3) [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_DomesticMidCapCommonCollectiveTrustFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
   
Employee Retirement Plan [Member] | Domestic Small Cap Common Collective Trust Fund [Member] | Fair Value [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 1,483us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_DomesticSmallCapCommonCollectiveTrustFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Employee Retirement Plan [Member] | Domestic Small Cap Common Collective Trust Fund [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_DomesticSmallCapCommonCollectiveTrustFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
   
Employee Retirement Plan [Member] | Domestic Small Cap Common Collective Trust Fund [Member] | Significant Other Observable Inputs (Level 2) [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 1,483us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_DomesticSmallCapCommonCollectiveTrustFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
   
Employee Retirement Plan [Member] | Domestic Small Cap Common Collective Trust Fund [Member] | Significant Unobservable Inputs (Level 3) [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_DomesticSmallCapCommonCollectiveTrustFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
   
Employee Retirement Plan [Member] | International Equity Common Collective Trust Fund [Member] | Fair Value [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 898us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_InternationalEquityCommonCollectiveTrustFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
   
Employee Retirement Plan [Member] | International Equity Common Collective Trust Fund [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_InternationalEquityCommonCollectiveTrustFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
   
Employee Retirement Plan [Member] | International Equity Common Collective Trust Fund [Member] | Significant Other Observable Inputs (Level 2) [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 898us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_InternationalEquityCommonCollectiveTrustFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
   
Employee Retirement Plan [Member] | International Equity Common Collective Trust Fund [Member] | Significant Unobservable Inputs (Level 3) [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_InternationalEquityCommonCollectiveTrustFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
   
Employee Retirement Plan [Member] | Fixed Income Common Collective Trust Fund [Member] | Fair Value [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period   2,354us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_FixedIncomeCommonCollectiveTrustFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember
 
Employee Retirement Plan [Member] | Fixed Income Common Collective Trust Fund [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period   0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_FixedIncomeCommonCollectiveTrustFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
 
Employee Retirement Plan [Member] | Fixed Income Common Collective Trust Fund [Member] | Significant Other Observable Inputs (Level 2) [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period   2,354us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_FixedIncomeCommonCollectiveTrustFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
 
Employee Retirement Plan [Member] | Fixed Income Common Collective Trust Fund [Member] | Significant Unobservable Inputs (Level 3) [Member]      
Plan assets at fair value [Roll Forward]      
Balance at end of period   0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= dcom_FixedIncomeCommonCollectiveTrustFundMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_EmployeeRetirementPlanMember
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member
 
BMP and Director Retirement Plan [Member]      
Net Periodic Benefit Cost [Abstract]      
Service Cost 0us-gaap_DefinedBenefitPlanServiceCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
0us-gaap_DefinedBenefitPlanServiceCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
0us-gaap_DefinedBenefitPlanServiceCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
Interest Cost 347us-gaap_DefinedBenefitPlanInterestCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
281us-gaap_DefinedBenefitPlanInterestCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
304us-gaap_DefinedBenefitPlanInterestCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
Expected return on plan assets 0us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
0us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
0us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
Amortization of unrealized loss 98us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
545us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
372us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
Net periodic cost 445us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
826us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
676us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
Reconciliation of Projected benefit obligation [Roll Forward]      
Accumulated benefit obligation at end of period 11,077us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
8,645us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
 
Projected benefit obligation at beginning of period 8,645us-gaap_DefinedBenefitPlanBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
8,958us-gaap_DefinedBenefitPlanBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
 
Actuarial adjustment 0us-gaap_DefinedBenefitPlanPlanAmendments
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
0us-gaap_DefinedBenefitPlanPlanAmendments
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
 
Service Cost 0us-gaap_DefinedBenefitPlanServiceCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
0us-gaap_DefinedBenefitPlanServiceCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
0us-gaap_DefinedBenefitPlanServiceCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
Interest Cost 347us-gaap_DefinedBenefitPlanInterestCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
281us-gaap_DefinedBenefitPlanInterestCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
304us-gaap_DefinedBenefitPlanInterestCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
Actuarial Loss 2,266us-gaap_DefinedBenefitPlanActuarialGainLoss
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
(413)us-gaap_DefinedBenefitPlanActuarialGainLoss
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
 
Benefit payments (181)us-gaap_DefinedBenefitPlanBenefitsPaid
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
(181)us-gaap_DefinedBenefitPlanBenefitsPaid
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
 
Projected benefit obligation at end of period 11,077us-gaap_DefinedBenefitPlanBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
8,645us-gaap_DefinedBenefitPlanBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
8,958us-gaap_DefinedBenefitPlanBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
Plan assets at fair value [Roll Forward]      
Balance at beginning of period 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
 
Contributions 181us-gaap_DefinedBenefitPlanContributionsByEmployer
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
181us-gaap_DefinedBenefitPlanContributionsByEmployer
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
 
Benefit payments (181)us-gaap_DefinedBenefitPlanBenefitsPaid
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
(181)us-gaap_DefinedBenefitPlanBenefitsPaid
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
 
Balance at end of period 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
Funded Status [Abstract]      
Deficiency of plan assets over projected benefit obligation (11,077)us-gaap_DefinedBenefitPlanPlansWithBenefitObligationsInExcessOfPlanAssetsAggregateBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
(8,645)us-gaap_DefinedBenefitPlanPlansWithBenefitObligationsInExcessOfPlanAssetsAggregateBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
 
Accrued retirement expense included in other liabilities (11,077)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
(8,645)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
 
Change in accumulated other comprehensive income (loss) [Abstract]      
Balance at beginning of period (1,081)us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
(2,039)us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
 
Adjustment for change in actuarial calculation 0us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
0us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
 
Amortization of unrealized loss 98us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
545us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
372us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
Loss recognized during the year (2,267)us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
413us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
 
Balance at the end of the period (3,250)us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
(1,081)us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
(2,039)us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
Period end component of accumulated other comprehensive loss (net of tax) 1,782us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeMinimumPensionLiabilityAfterTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
593us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeMinimumPensionLiabilityAfterTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
 
Expected Future Benefit Payments [Abstract]      
2015 792us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
   
2016 831us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
   
2017 819us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
   
2018 807us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
   
2019 792us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
   
2020 to 2024 3,870us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpAndDirectorRetirementPlanMember
   
Postretirement Benefit Plans [Member]      
Net Periodic Benefit Cost [Abstract]      
Service Cost 41us-gaap_DefinedBenefitPlanServiceCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
60us-gaap_DefinedBenefitPlanServiceCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
83us-gaap_DefinedBenefitPlanServiceCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Interest Cost 232us-gaap_DefinedBenefitPlanInterestCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
227us-gaap_DefinedBenefitPlanInterestCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
236us-gaap_DefinedBenefitPlanInterestCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Expected return on plan assets 0us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
0us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
0us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Amortization of unrealized loss 0us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
48us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
2us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Net periodic cost 273us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
335us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
321us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Reconciliation of Projected benefit obligation [Roll Forward]      
Accumulated benefit obligation at end of period 4,284us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
4,998us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Projected benefit obligation at beginning of period 4,998us-gaap_DefinedBenefitPlanBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
6,191us-gaap_DefinedBenefitPlanBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Service Cost 41us-gaap_DefinedBenefitPlanServiceCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
60us-gaap_DefinedBenefitPlanServiceCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
83us-gaap_DefinedBenefitPlanServiceCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Interest Cost 232us-gaap_DefinedBenefitPlanInterestCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
227us-gaap_DefinedBenefitPlanInterestCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
236us-gaap_DefinedBenefitPlanInterestCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Actuarial Loss 309us-gaap_DefinedBenefitPlanActuarialGainLoss
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
(1,352)us-gaap_DefinedBenefitPlanActuarialGainLoss
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Benefit payments (95)us-gaap_DefinedBenefitPlanBenefitsPaid
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
(128)us-gaap_DefinedBenefitPlanBenefitsPaid
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Plan amendments (1,201)us-gaap_DefinedBenefitPlanOtherChanges
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
0us-gaap_DefinedBenefitPlanOtherChanges
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Projected benefit obligation at end of period 4,284us-gaap_DefinedBenefitPlanBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
4,998us-gaap_DefinedBenefitPlanBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
6,191us-gaap_DefinedBenefitPlanBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Plan assets at fair value [Roll Forward]      
Balance at beginning of period 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Contributions 95us-gaap_DefinedBenefitPlanContributionsByEmployer
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
128us-gaap_DefinedBenefitPlanContributionsByEmployer
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Benefit payments (95)us-gaap_DefinedBenefitPlanBenefitsPaid
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
(128)us-gaap_DefinedBenefitPlanBenefitsPaid
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Balance at end of period 0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
0us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Funded Status [Abstract]      
Deficiency of plan assets over projected benefit obligation 4,284us-gaap_DefinedBenefitPlanPlansWithBenefitObligationsInExcessOfPlanAssetsAggregateBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
(4,998)us-gaap_DefinedBenefitPlanPlansWithBenefitObligationsInExcessOfPlanAssetsAggregateBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Accrued retirement expense included in other liabilities (4,284)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
(4,998)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Change in accumulated other comprehensive income (loss) [Abstract]      
Balance at beginning of period 400us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
(1,000)us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Amortization of unrealized loss 0us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
48us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
2us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Loss recognized during the year (309)us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
1,352us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
New Past Service Liability During the Year 1,201us-gaap_DefinedBenefitPlanOtherChanges
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
0us-gaap_DefinedBenefitPlanOtherChanges
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Balance at the end of the period 1,292us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
400us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
(1,000)us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Period end component of accumulated other comprehensive loss (net of tax) (709)us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeMinimumPensionLiabilityAfterTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
(219)us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeMinimumPensionLiabilityAfterTax
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Employer contributions in next fiscal year 145us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInNextFiscalYear
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
   
Actuarial losses anticipated to be recognized as component of net periodic cost 0us-gaap_DefinedBenefitPlanAmountToBeAmortizedFromAccumulatedOtherComprehensiveIncomeLossNextFiscalYear
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
   
Assumptions Used in Calculations [Abstract]      
Discount rate used for net periodic cost (credit) (in hundredths) 4.72%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
3.72%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
4.28%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Discount rate used to determine benefit obligation at period end (in hundredths) 3.80%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
4.72%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
3.72%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Rate of increase in compensation levels used for net periodic cost (credit) (in hundredths) 3.50%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostRateOfCompensationIncrease
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
3.50%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostRateOfCompensationIncrease
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
3.50%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostRateOfCompensationIncrease
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Rate of increase in compensation levels used to determine benefit obligation at period end (in hundredths) 3.50%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
3.50%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
3.50%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Expected Future Benefit Payments [Abstract]      
2015 145us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
   
2016 155us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
   
2017 161us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
   
2018 168us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
   
2019 171us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
   
2020 to 2024 893us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
   
Assumed Health Care Cost Trend Rates [Abstract]      
Effect of one percentage point increase on net periodic cost 4us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointIncreaseOnServiceAndInterestCostComponents
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
   
Effect of one percentage point decrease on net periodic cost (5)us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointDecreaseOnServiceAndInterestCostComponents1
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
   
Health care cost trend rate assumed for next fiscal year (in hundredths) 6.50%us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
   
Ultimate health care cost trend rate (in hundredths) 5.00%us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
   
Effect of one percentage point decrease on accumulated postretirement benefit obligation (140)us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointDecreaseOnAccumulatedPostretirementBenefitObligation1
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
   
Effect of one percentage point increase on accumulated postretirement benefit obligation 153us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointIncreaseOnAccumulatedPostretirementBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
   
Director Retirement Plan [Member]      
Change in accumulated other comprehensive income (loss) [Abstract]      
Employer contributions in next fiscal year 188us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInNextFiscalYear
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_DirectorRetirementPlanMember
   
Actuarial losses anticipated to be recognized as component of net periodic cost 172us-gaap_DefinedBenefitPlanAmountToBeAmortizedFromAccumulatedOtherComprehensiveIncomeLossNextFiscalYear
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_DirectorRetirementPlanMember
   
Assumptions Used in Calculations [Abstract]      
Discount rate used for net periodic cost (credit) (in hundredths) 4.22%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_DirectorRetirementPlanMember
3.30%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_DirectorRetirementPlanMember
3.84%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_DirectorRetirementPlanMember
Discount rate used to determine benefit obligation at period end (in hundredths) 3.49%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_DirectorRetirementPlanMember
4.22%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_DirectorRetirementPlanMember
3.30%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_DirectorRetirementPlanMember
BMP [Member]      
Change in accumulated other comprehensive income (loss) [Abstract]      
Defined Contribution cost recognized 1,789us-gaap_DefinedContributionPlanCostRecognized
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpMember
2,377us-gaap_DefinedContributionPlanCostRecognized
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpMember
1,935us-gaap_DefinedContributionPlanCostRecognized
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpMember
Employer contributions in next fiscal year 604us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInNextFiscalYear
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpMember
   
Actuarial losses anticipated to be recognized as component of net periodic cost 70us-gaap_DefinedBenefitPlanAmountToBeAmortizedFromAccumulatedOtherComprehensiveIncomeLossNextFiscalYear
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpMember
   
Assumptions Used in Calculations [Abstract]      
Discount rate used for net periodic cost (credit) (in hundredths) 4.00%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpMember
3.09%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpMember
3.77%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpMember
Discount rate used to determine benefit obligation at period end (in hundredths) 3.39%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpMember
4.00%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpMember
3.09%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpMember
Investments in the Holding Company's common stock $ 13,232dcom_InvestmentsInHoldingCompanySCommonStock
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpMember
$ 13,595dcom_InvestmentsInHoldingCompanySCommonStock
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= dcom_BmpMember