Disclosures about Oil and Natural Gas Activities (Unaudited)--Standardized Measure of Discounted Future Net Cash Flows (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items]
Future cash flows	$ 10,660,532	$ 9,690,171	$ 10,737,829
Future production costs	3,841,723	3,737,069	4,061,713
Future development and abandonment costs	1,506,585	1,172,786	1,202,438
Future income tax provisions	1,328,925	1,223,036	1,653,666
Net future cash flows	3,983,299	3,557,280	3,820,012
Less effect of 10% discount factor	(2,239,527)	(2,033,599)	(2,222,100)
Standardized measure of discounted future net cash flows	$ 1,743,772	$ 1,523,681	$ 1,597,912