Supplemental Oil and Gas Information (Unaudited) Discounted Future Cash Flows of Proved Reserves (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
U.S. [Member]
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items]
Future revenue	$ 3,825,944	$ 3,980,643	$ 11,647,002
Future production costs	(2,022,977)	(2,552,863)	(5,496,246)
Future development costs	(212,280)	(239,532)	(1,125,641)
Future income taxes	(134,418)	81,847	(1,229,968)
Future net cash flows	1,456,269	1,270,095	3,795,147
10% discount	(801,116)	(667,738)	(2,286,449)
Standardized measure of discounted future cash flows relating to proved reserves	655,153	602,357	1,508,698
Canada [Member]
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items]
Future revenue	656,984	472,539	1,055,711
Future production costs	(385,776)	(324,424)	(463,852)
Future development costs	(79,525)	(56,354)	(146,658)
Future income taxes	59,294	80,206	(44,183)
Future net cash flows	250,977	171,967	401,018
10% discount	(83,082)	(59,204)	(174,863)
Standardized measure of discounted future cash flows relating to proved reserves	167,895	112,763	226,155
Consolidated [Member]
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items]
Future revenue	4,482,928	4,453,182	12,702,713
Future production costs	(2,408,753)	(2,877,287)	(5,960,098)
Future development costs	(291,805)	(295,886)	(1,272,299)
Future income taxes	(75,124)	162,053	(1,274,151)
Future net cash flows	1,707,246	1,442,062	4,196,165
10% discount	(884,198)	(726,942)	(2,461,312)
Standardized measure of discounted future cash flows relating to proved reserves	$ 823,048	$ 715,120	$ 1,734,853