Change in Accounting Principle (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Balance Sheet Disclosures
Accounts receivable: Crude oil resales	$ 46,502,000	$ 5,166,000
Total current assets	4,470,265,000	3,920,746,000
Total assets	10,328,997,000	9,576,243,000
Accounts payable	1,314,151,000	1,504,694,000
Total current liabilities	1,654,444,000	1,890,683,000
Total liabilities and equity	10,328,997,000	9,576,243,000
Statement of Cash Flows Disclosures
(Increase) decrease in accounts receivable	71,627,000	373,591,000	43,437,000
Increase (decrease) in accounts payable	(194,051,000)	(251,428,000)	70,279,000
Receivables, reported as a reduction of accounts payable	723,400,000
As Originally Reported
Balance Sheet Disclosures
Accounts receivable: Crude oil resales		743,544,000
Total current assets		4,659,124,000
Total assets		10,314,621,000
Accounts payable		2,243,072,000
Total current liabilities		2,629,061,000
Total liabilities and equity		10,314,621,000
Statement of Cash Flows Disclosures
(Increase) decrease in accounts receivable		286,737,000	(228,466,000)
Increase (decrease) in accounts payable		(164,574,000)	342,182,000
Effect of Change
Balance Sheet Disclosures
Accounts receivable: Crude oil resales		(738,378,000)
Total current assets		(738,378,000)
Total assets		(738,378,000)
Accounts payable		(738,378,000)
Total current liabilities		(738,378,000)
Total liabilities and equity		(738,378,000)
Statement of Cash Flows Disclosures
(Increase) decrease in accounts receivable		86,854,000	271,903,000
Increase (decrease) in accounts payable		$ (86,854,000)	$ (271,903,000)