Joint Interest and Other Receivables (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Joint Interest Receivables
Settlement period for bills under operating agreements	30 days
Accrued interest on investment securities	$ 11,209	$ 3,647
Vendors' receivables	3,789	1,526
Other	3,342	1,795
Total joint interest and other receivables	71,687	61,592
Partners in the U.S. Gulf of Mexico
Joint Interest Receivables
Receivable attributable to joint interest partners	50,161	52,439
Partners in West Africa
Joint Interest Receivables
Receivable attributable to joint interest partners	$ 3,186	$ 2,185