Oil and Natural Gas Activities--Costs Incurred Footnote (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Oil and Gas In Process Activities [Line Items]
Exploration costs	$ 77,507	[1]	$ 54,432	[1]	$ 57,016	[1]
Enhanced Oil Recovery
Oil and Gas In Process Activities [Line Items]
Exploration costs	$ 37,344		$ 52,188		$ 33,030

[1] Includes $37,344, $52,188, and $33,030 of EOR costs in 2013, 2012, and 2011, respectively.