Risk Management and Derivative Instruments (Details)	Sep. 30, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Contracts Using Fair Value Method	0

Number of contracts that are accounted for using the fair value method of accounting.

No definition available.

Name:	dgas_Dgas_Contractsusingfairvaluemethod
Namespace Prefix:	dgas_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant