REGULATORY MATTERS (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Bank [Member]
Summary of actual capital amounts and ratios [Abstract]
Tier One Risk Based Capital Amount-Average Assets Ratio	$ 440,374	$ 406,910
Common Equity Tier 1 Capital	440,374
Tier One Risk Based Capital	440,374	406,910
Total capital, Amount	458,938	425,428
Tier One Risk Based Capital-Average Assets Ratio Required For Capital Adequacy	194,314
Common Equity Tier 1 Capital Amount Required for Capital Adequacy	171,628
Tier One Risk Based Capital Required for Capital Adequacy	228,838	131,994
Capital Required for Capital Adequacy	305,117	263,988
Tier 1 Risk Based Capital Average Assets ratio Required to be Well Capitalized	242,892
Common Equity Tier 1 Capital Amount Required to be Well Capitalized	247,908
Tier One Risk Based Capital Required to be Well Capitalized	305,117	197,991
Capital Required to be Well Capitalized	$ 381,397	$ 329,985
Risk Based Ratios [Abstract]
Tier 1 Capital as a percentage of average assets	9.17%
Common equity tier 1 capital ratio	11.55%
Tier One Risk Based Capital to Risk Weighted Assets (in hundredths)	11.55%	12.33%
Total Capital to Risk Weighted Assets (in hundredths)	12.03%	12.89%
Tier 1 Capital as a percentage of average assets required to be adequately capitalized	4.00%
Common Equity Tier 1 Ratio Required to be Adequately Capitalized	4.50%
Tier One Risk Based Capital Required for Capital Adequacy (in hundredths)	6.00%	4.00%
Total Capital Required for Capital Adequacy (in hundredths)	8.00%	8.00%
Tier 1 capital as a percentage of total assets to be well capitalized	5.00%
Common Equity Tier 1 Capital Required to Be Well Capitalized	6.50%
Tier One Risk Based Capital Required to be Well Capitalized (in hundredths)	8.00%	6.00%
Total Capital Required to be Well Capitalized (in hundredths)	10.00%	10.00%
Tangible Capital		$ 406,910
Tangible Capital to Tangible Assets		9.20%
Tangible Capital Required for Capital Adequacy		$ 176,998
Tangible Capital Required for Capital Adequacy to Tangible Assets		4.00%
Tangible Capital Required to Be Well Capitalized		$ 221,247
Tangible Capital ratio required to be well capitalized		5.00%
Tier 1 Capital ratio as a percentage of tangible assets		9.20%
Tier 1 Capital Amount Required to Be Adequately Capitalized for ratio to total tangible assets		$ 176,998
Tier 1 risk based capital ratio required to be adequately capitalized		4.00%
Tier 1 capital required to be deemed well capitalized under ratio to total tangible assets		$ 221,247
Tier 1 capital ratio of total tangible assets required to be well capitalized		5.00%
Consolidated Company [Member]
Summary of actual capital amounts and ratios [Abstract]
Tier One Risk Based Capital Amount-Average Assets Ratio	$ 447,111
Common Equity Tier 1 Capital	447,111
Tier One Risk Based Capital	515,626
Total capital, Amount	534,190
Tier One Risk Based Capital-Average Assets Ratio Required For Capital Adequacy	195,008
Common Equity Tier 1 Capital Amount Required for Capital Adequacy	172,456
Tier One Risk Based Capital Required for Capital Adequacy	229,941
Capital Required for Capital Adequacy	$ 306,588
Risk Based Ratios [Abstract]
Tier 1 Capital as a percentage of average assets	10.70%
Common equity tier 1 capital ratio	11.67%
Tier One Risk Based Capital to Risk Weighted Assets (in hundredths)	13.45%
Total Capital to Risk Weighted Assets (in hundredths)	13.94%
Tier 1 Capital as a percentage of average assets required to be adequately capitalized	4.00%
Common Equity Tier 1 Ratio Required to be Adequately Capitalized	4.50%
Tier One Risk Based Capital Required for Capital Adequacy (in hundredths)	6.00%
Total Capital Required for Capital Adequacy (in hundredths)	8.00%

Common Equity Tier 1 Capital determined in accordance with the Basel III regulatory rules.

No definition available.

Name:	dcom_CommonEquityTier1Capital
Namespace Prefix:	dcom_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount of Common Equity Tier 1 Capital Required for capital adequacy purposes for the ratio of Common Equity Tier 1 Capital to Total risk based assets calculated under the Basel III regulatory rules.

+ References

No definition available.

+ Details

Name:	dcom_CommonEquityTier1CapitalAmountRequiredForCapitalAdequacy
Namespace Prefix:	dcom_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount of Common Equity Tier 1 Capital Required to be well capitalized under the ratio of Common Equity Tier 1 Capital to Total risk weighted assets calculated under the Basel III regulatory rules.

+ References

No definition available.

+ Details

Name:	dcom_CommonEquityTier1CapitalAmountRequiredToBeWellCapitalized
Namespace Prefix:	dcom_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The ratio (shown as a percentage) of common equity tier 1 capital to risk weighted assets required to be well capitalized, and calculated in accordance with the Basel III regulatory rules.

+ References

No definition available.

+ Details

Name:	dcom_CommonEquityTier1CapitalRequiredToBeWellCapitalized
Namespace Prefix:	dcom_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The ratio (shown as a percentage) of common equity tier 1 capital to risk weighted assets to be considered adequately capitalized, and calculated in accordance with the Basel III regulatory rules.

+ References

No definition available.

+ Details

Name:	dcom_CommonEquityTier1RatioRequiredToBeAdequatelyCapitalized
Namespace Prefix:	dcom_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The ratio (shown as a percentage) of common equity tier 1 capital to risk weighted assets calculated in accordance with the Basel III regulatory rules.

+ References

No definition available.

+ Details

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

- References

No definition available.

+ Details

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

- Definition

The ratio of tangible capital to tangible (adjusted) assets required to be considered well capitalized in accordance with the Basel I banking regulations.

+ References

No definition available.

+ Details

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

- Definition

The amount of tangible capital (as defined under Basel I regulations) required to be considered well capitalized, in accordance with the Basel I banking regulations.

+ References

No definition available.

+ Details

Name:	dcom_TangibleCapitalRequiredToBeWellCapitalized
Namespace Prefix:	dcom_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

The total amount of Tier 1 risk based capital required to be deemed adequately capitalized for the ratio of Tier 1 capital to total tangible (adjusted ) assets, as calculated under the Basel I regulations.

+ References

No definition available.

+ Details

Name:	dcom_Tier1CapitalAmountRequiredToBeAdequatelyCapitalizedForRatioToTotalTangibleAssets
Namespace Prefix:	dcom_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

The ratio (shown as a percentage) of tier 1 capital to total average assets calculated in accordance with the Basel III regulatory rules.

+ References

No definition available.

+ Details

Name:	dcom_Tier1CapitalAsAPercentageOfAverageAssets
Namespace Prefix:	dcom_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The ratio (shown as a percentage) of tier 1 capital to total average assets to be considered adequately capitalized, and calculated in accordance with the Basel III regulatory rules.

+ References

No definition available.

+ Details

Name:	dcom_Tier1CapitalAsAPercentageOfAverageAssetsRequiredToBeAdequatelyCapitalized
Namespace Prefix:	dcom_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The ratio (shown as a percentage) of tier 1 capital to total average assets required to be considered well capitalized, and calculated in accordance with the Basel III regulatory rules.

+ References

No definition available.

+ Details

Name:	dcom_Tier1CapitalAsAPercentageOfTotalAssetsToBeWellCapitalized
Namespace Prefix:	dcom_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The ratio of Tier 1 risk based capital as a percentage of total tangible (adjusted) assets, calculated in accordance with Basel I banking regulations.

+ References

No definition available.

+ Details

Name:	dcom_Tier1CapitalRatioAsAPercentageOfTangibleAssets
Namespace Prefix:	dcom_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The ratio of Tier 1 risk based assets as a percentage of total tangible (adjusted assets) required to be deemed well capitalized in accordance with the Basel I banking regulations.

+ References

No definition available.

+ Details

Name:	dcom_Tier1CapitalRatioOfTotalTangibleAssetsRequiredToBeWellCapitalized
Namespace Prefix:	dcom_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The total amount of Tier 1 risk based capital required to be deemed well capitalized for the ratio of Tier 1 capital to total tangible (adjusted ) assets, as calculated under the Basel I regulations.

+ References

No definition available.

+ Details

Name:	dcom_Tier1CapitalRequiredToBeDeemedWellCapitalizedUnderRatioToTotalTangibleAssets
Namespace Prefix:	dcom_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of Tier 1 Capital required to be well capitalized under the calculation of Tier 1 capital to average assets in accordance with the Basel III regulatory rules.

+ References

No definition available.

+ Details

Name:	dcom_Tier1RiskBasedCapitalAverageAssetsRatioRequiredToBeWellCapitalized
Namespace Prefix:	dcom_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The ratio of Tier 1 risk based capital as a percentage of total tangible (adjusted) assets required to be deemed adequately capitalized.

+ References

No definition available.

+ Details

Name:	dcom_Tier1RiskBasedCapitalRatioRequiredToBeAdequatelyCapitalized
Namespace Prefix:	dcom_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of Tier 1 Capital required for capital adequacy purposes under the calculation of Tier 1 capital to average assets in accordance with the Basel III regulatory rules.

+ References

No definition available.

+ Details

Name:	dcom_TierOneRiskBasedCapitalAverageAssetsRatioRequiredForCapitalAdequacy
Namespace Prefix:	dcom_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

Tier 1 Risk Based Capital as defined in the regulations and utilized for the calculation of Tier 1 risk weighted assets to total average assets in accordance with the Basel III rules.

+ References

No definition available.

+ Details

Name:	dcom_TierOneRiskBasedCapitalTotalAssets
Namespace Prefix:	dcom_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount of total capital as defined in the regulations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6490092&loc=d3e47304-110998

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1H
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1H
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=6490092&loc=d3e47080-110998

+ Details

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

- Definition

The minimum amount of Total Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1H
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826

+ Details

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

- Definition

The minimum Total risk based capital ratio (total capital divided by risk weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1H
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958570-112826

+ Details

Name:	us-gaap_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of Total Capital required to be categorized as well as capitalized under the regulatory framework for prompt corrective action.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826

+ Details

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

- Definition

The Total risk based capital ratio (total capital divided by risk weighted assets) required to be categorized as "well capitalized", in the regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Total Capital divided by risk weighted assets as defined in the regulations.

+ References

+ Details

Name:	us-gaap_CapitalToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- References

No definition available.

+ Details

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

- Definition

Tangible capital as defined in the regulations (generally includes outstanding stock plus retained earnings) for banking institutions subject to Office of Thrift Supervision (OTS) capital requirements.

+ References

+ Details

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

- Definition

The minimum amount of tangible capital required under the regulatory framework for prompt corrective action.

+ References

+ Details

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

- Definition

The minimum amount of Tangible Capital divided by tangible assets (Tangible Capital Ratio) as defined in the regulations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958570-112826

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1H
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826

+ Details

Name:	us-gaap_TangibleCapitalRequiredForCapitalAdequacyToTangibleAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Tangible Capital divided by Tangible assets as defined in the regulations.

+ References

+ Details

Name:	us-gaap_TangibleCapitalToTangibleAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Tier 1 Risk Based Capital as defined in the regulations.

+ References

+ Details

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

- Definition

The minimum amount of Tier 1 Risk Based Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action.

+ References

+ Details

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

- Definition

The minimum Tier One Capital Ratio (Tier one capital divided by risk-weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958568-112826

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=35709795&loc=SL5958570-112826

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1H
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=35709795&loc=d3e65071-112826

+ Details

Name:	us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of Tier 1 Risk Based Capital required to be categorized as well capitalized under the regulatory framework for prompt corrective action.

+ References

+ Details

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

- Definition

The Tier 1 capital ratio (Tier 1 capital divided by risk weighted assets) required to be categorized as "well capitalized" under the regulatory framework for prompt corrective action.

+ References

+ Details

Name:	us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Tier 1 capital divided by risk weighted assets as defined by regulations.

+ References

+ Details

Name:	us-gaap_TierOneRiskBasedCapitalToRiskWeightedAssets
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	dei_LegalEntityAxis=us-gaap_SubsidiariesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=dcom_ConsolidatedCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: