FAIR VALUE OF FINANCIAL INSTRUMENTS, Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) $ in Thousands	Sep. 30, 2017 USD ($)	Dec. 31, 2016 USD ($) Security
Financial Liabilities [Abstract]
Impaired loans measured at fair value	$ 0	$ 0
Trust Preferred Securities, Number \| Security		7
Recurring [Member]
Trading securities (Registered Mutual Funds) [Abstract]
Domestic Equity Mutual Funds	435	$ 873
International Equity Mutual Funds	115	213
Fixed Income Mutual Funds	2,125	5,867
Registered Mutual Funds [Abstract]
Domestic Equity Mutual Funds	1,479	1,356
International Equity Mutual Funds	441	377
Fixed Income Mutual Funds	2,114	2,162
Pass-through MBS issued by GSEs	16,684	372
Agency CMOs	10,697	3,186
Derivative - interest rate product	2,973	3,228
Financial Liabilities [Abstract]
Derivative - interest rate product	50
Recurring [Member] \| Level 1 Inputs [Member]
Trading securities (Registered Mutual Funds) [Abstract]
Domestic Equity Mutual Funds	435	873
International Equity Mutual Funds	115	213
Fixed Income Mutual Funds	2,125	5,867
Registered Mutual Funds [Abstract]
Domestic Equity Mutual Funds	1,479	1,356
International Equity Mutual Funds	441	377
Fixed Income Mutual Funds	2,114	2,162
Pass-through MBS issued by GSEs	0	0
Agency CMOs	0	0
Derivative - interest rate product	0	0
Financial Liabilities [Abstract]
Derivative - interest rate product	0
Recurring [Member] \| Level 2 Inputs [Member]
Trading securities (Registered Mutual Funds) [Abstract]
Domestic Equity Mutual Funds	0	0
International Equity Mutual Funds	0	0
Fixed Income Mutual Funds	0	0
Registered Mutual Funds [Abstract]
Domestic Equity Mutual Funds	0	0
International Equity Mutual Funds	0	0
Fixed Income Mutual Funds	0	0
Pass-through MBS issued by GSEs	16,684	372
Agency CMOs	10,697	3,186
Derivative - interest rate product	2,973	3,228
Financial Liabilities [Abstract]
Derivative - interest rate product	50
Recurring [Member] \| Level 3 Inputs [Member]
Trading securities (Registered Mutual Funds) [Abstract]
Domestic Equity Mutual Funds	0	0
International Equity Mutual Funds	0	0
Fixed Income Mutual Funds	0	0
Registered Mutual Funds [Abstract]
Domestic Equity Mutual Funds	0	0
International Equity Mutual Funds	0	0
Fixed Income Mutual Funds	0	0
Pass-through MBS issued by GSEs	0	0
Agency CMOs	0	0
Derivative - interest rate product	0	0
Financial Liabilities [Abstract]
Derivative - interest rate product	0
Nonrecurring [Member]
Financial Liabilities [Abstract]
Assets measured at fair value	$ 0	$ 0

No definition available.

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

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Registered Domestic Equity Mutual Funds categorized as Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

+ References

No definition available.