DERIVATIVES AND HEDGING ACTIVITIES, Offsetting of Derivative Liabilities (Details) $ in Thousands	12 Months Ended
Dec. 31, 2017 USD ($) Provision
DERIVATIVES AND HEDGING ACTIVITIES [Abstract]
Fair value of derivative liability, including accrued interest \| $	$ 4,026
Number of provisions breached \| Provision	0

Fair value of a financial liability or contract, including accrued interest, with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

No definition available.

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