Accumulated Other Comprehensive Income (Loss) - Schedule of Changes in Accumulated Other Comprehensive Income Loss (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, net of tax	$ (2,062)	$ 28,833
Other comprehensive income (loss) before reclassifications:
Change in fair value of derivatives	136,097	(26,945)
Foreign currency translations	(2,801)	(667)
Income tax effect	(48,995)	9,701
Net of tax	84,301	(17,911)
Amounts reclassified from accumulated other comprehensive income:
Net of tax	(1,076)	12,984
Other comprehensive income (loss), net of tax	85,377	(30,895)
Ending balance, net of tax	83,315	(2,062)
Reclassification out of Accumulated Other Comprehensive Income [Member]
Amounts reclassified from accumulated other comprehensive income:
Operating revenue: oil/gas production	526	20,289
Derivative expense, net	(2,208)
Income tax effect	606	(7,305)
Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, net of tax	(1,395)	28,833	21,868
Other comprehensive income (loss) before reclassifications:
Change in fair value of derivatives	136,097	(26,945)	41,209
Income tax effect	(48,995)	9,701	(14,836)
Net of tax	87,102	(17,244)	26,373
Amounts reclassified from accumulated other comprehensive income:
Net of tax	(1,076)	12,984	19,408
Other comprehensive income (loss), net of tax	88,178	(30,228)	6,965
Ending balance, net of tax	86,783	(1,395)	28,833
Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Amounts reclassified from accumulated other comprehensive income:
Operating revenue: oil/gas production	526	20,289	30,326
Derivative expense, net	(2,208)
Income tax effect	606	(7,305)	(10,918)
Foreign Currency Items [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, net of tax	(667)
Other comprehensive income (loss) before reclassifications:
Foreign currency translations	(2,801)	(667)
Net of tax	(2,801)	(667)
Amounts reclassified from accumulated other comprehensive income:
Other comprehensive income (loss), net of tax	(2,801)	(667)
Ending balance, net of tax	$ (3,468)	$ (667)