Supplemental Oil and Gas Information (Unaudited) Results from Producing Activities (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Capitalized Costs Relating to Oil and Gas Producing Activities, by Geographic Area [Line Items]
Income (loss) before income taxes	$ 176,168	$ (2,648,176)	$ 147,909
U.S. [Member]
Capitalized Costs Relating to Oil and Gas Producing Activities, by Geographic Area [Line Items]
Natural gas, NGL and oil revenue	331,964	538,902	673,041
Operating expense	167,425	226,542	267,890
Depletion expense	34,995	116,005	164,493
Impairment expense		2,152,128	0
Income (loss) before income taxes	129,544	(1,955,773)	240,658
Income tax expense (benefit)	45,340	(684,521)	84,230
Results of midstream operations, net of income tax	84,204	(1,271,252)	156,428
Canada [Member]
Capitalized Costs Relating to Oil and Gas Producing Activities, by Geographic Area [Line Items]
Natural gas, NGL and oil revenue	131,527	92,045	127,502
Operating expense	80,475	60,501	54,770
Depletion expense	5,362	24,897	38,228
Impairment expense		465,935	49,063
Income (loss) before income taxes	45,690	(459,288)	(14,559)
Income tax expense (benefit)	11,514	(114,822)	(4,222)
Results of midstream operations, net of income tax	34,176	(344,466)	(10,337)
Consolidated [Member]
Capitalized Costs Relating to Oil and Gas Producing Activities, by Geographic Area [Line Items]
Natural gas, NGL and oil revenue	463,491	630,947	800,543
Operating expense	247,900	287,043	322,660
Depletion expense	40,357	140,902	202,721
Impairment expense		2,618,063	49,063
Income (loss) before income taxes	175,234	(2,415,061)	226,099
Income tax expense (benefit)	56,854	(799,343)	80,008
Results of midstream operations, net of income tax	$ 118,380	$ (1,615,718)	$ 146,091