Price Risk Management Counterparties Representing 10% or More (Details)	Jun. 30, 2012	Dec. 31, 2011
Assets from price risk management activities:
Counterparty A	12.00%	0.00%
Counterparty B	12.00%	7.00%
Counterparty C	11.00%	19.00%
Counterparty D	11.00%	6.00%
Counterparty E	7.00%	16.00%
Counterparty F	2.00%	13.00%
Concentration of Risk, Derivative Instruments, Assets	55.00%	61.00%
Liabilities from price risk management activities:
Counterparty B PRM Liabilities	22.00%	23.00%
Counterparty G	11.00%	10.00%
Concentration of Risk, Derivative Instruments, Liabilities	33.00%	33.00%