FAIR VALUE OF FINANCIAL INSTRUMENTS, Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - Recurring [Member] - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Marketable equity securities (Registered Mutual Funds) [Abstract]
Domestic Equity Mutual Funds	$ 1,863
International Equity Mutual Funds	538
Fixed Income Mutual Funds	4,032
Trading securities (Registered Mutual Funds) [Abstract]
Domestic Equity Mutual Funds		$ 460
International Equity Mutual Funds		120
Fixed Income Mutual Funds		2,135
Registered Mutual Funds [Abstract]
Domestic Equity Mutual Funds		1,512
International Equity Mutual Funds		445
Fixed Income Mutual Funds		2,049
Pass-through MBS issued by GSEs	237,365	72,629
Agency CMOs	117,045	278,755
Derivative - interest rate product	6,117	4,041
Financial Liabilities [Abstract]
Derivative - interest rate product	78
Level 1 Inputs [Member]
Marketable equity securities (Registered Mutual Funds) [Abstract]
Domestic Equity Mutual Funds	1,863
International Equity Mutual Funds	538
Fixed Income Mutual Funds	4,032
Trading securities (Registered Mutual Funds) [Abstract]
Domestic Equity Mutual Funds		460
International Equity Mutual Funds		120
Fixed Income Mutual Funds		2,135
Registered Mutual Funds [Abstract]
Domestic Equity Mutual Funds		1,512
International Equity Mutual Funds		445
Fixed Income Mutual Funds		2,049
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
Level 2 Inputs [Member]
Marketable equity securities (Registered Mutual Funds) [Abstract]
Domestic Equity Mutual Funds	0
International Equity Mutual Funds	0
Fixed Income Mutual Funds	0
Trading securities (Registered Mutual Funds) [Abstract]
Domestic Equity Mutual Funds		0
International Equity Mutual Funds		0
Fixed Income Mutual Funds		0
Registered Mutual Funds [Abstract]
Domestic Equity Mutual Funds		0
International Equity Mutual Funds		0
Fixed Income Mutual Funds		0
Pass-through MBS issued by GSEs	237,365	72,629
Agency CMOs	117,045	278,755
Derivative - interest rate product	6,117	4,041
Financial Liabilities [Abstract]
Derivative - interest rate product	78
Level 3 Inputs [Member]
Marketable equity securities (Registered Mutual Funds) [Abstract]
Domestic Equity Mutual Funds	0
International Equity Mutual Funds	0
Fixed Income Mutual Funds	0
Trading securities (Registered Mutual Funds) [Abstract]
Domestic Equity Mutual Funds		0
International Equity Mutual Funds		0
Fixed Income Mutual Funds		0
Registered Mutual Funds [Abstract]
Domestic Equity Mutual Funds		0
International Equity Mutual Funds		0
Fixed Income Mutual Funds		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

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.