Derivative Instruments (Details 3) (Parenthetical) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Before-tax effect of derivative instruments not designated as hedging instruments on the consolidated statements of operations
Price risk management activities	$ (2,804)	$ 5,772

The realized and unrealized gains/(losses) on commodity derivative contracts during the period.

No definition available.

Name:	dble_PriceRiskManagementActivitiesNet
Namespace Prefix:	dble_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration