Concentrations (Details)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Conoco, Inc. [Member]
Sales to Major Customers
Customers from whom 10% or more revenue derived	28.00%	26.00%	27.00%
Hess Corporation [Member]
Sales to Major Customers
Customers from whom 10% or more revenue derived		11.00%	11.00%
Less than 10 %	Less than 10 %
Sequent Energy Management LP [Member]
Sales to Major Customers
Customers from whom 10% or more revenue derived		10.00%	13.00%
Less than 10 %	Less than 10 %
Shell Trading (US) Company [Member]
Sales to Major Customers
Customers from whom 10% or more revenue derived	46.00%	40.00%	34.00%