Summary of Significant Accounting Policies Major Customers (Details) (Sales)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Oil | ExxonMobil Oil Corporation
Revenue, Major Customer
Concentration Risk, Percentage	43.00%	43.00%	44.00%
Oil | Shell Trading (US) Company
Revenue, Major Customer
Concentration Risk, Percentage	13.00%	14.00%	14.00%
Oil | Enterprise Crude Oil LLC
Revenue, Major Customer
Concentration Risk, Percentage	9.00%	8.00%	4.00%
Oil | HollyFrontier Corporation
Revenue, Major Customer
Concentration Risk, Percentage	9.00%	8.00%	9.00%
Electricity Generation | Pacific Gas and Electric Company
Revenue, Major Customer
Concentration Risk, Percentage	54.00%	59.00%	55.00%
Electricity Generation | Southern California Edison
Revenue, Major Customer
Concentration Risk, Percentage	46.00%	41.00%	45.00%