Schedule of Changes In Accumulated Other Comprehensive Income Loss (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, net of tax	$ 28,833
Other comprehensive income (loss) before reclassifications:
Change in fair value of derivatives	(26,945)
Foreign currency translations	(667)
Income tax effect	9,701
Net of tax	(17,911)
Amounts reclassified from accumulated other comprehensive income:
Net of tax	12,984
Other comprehensive income (loss), net of tax	(30,895)
Ending balance, net of tax	(2,062)
Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, net of tax	28,833	21,868	(14,204)
Other comprehensive income (loss) before reclassifications:
Change in fair value of derivatives	(26,945)	41,209	43,089
Income tax effect	9,701	(14,836)	(15,512)
Net of tax	(17,244)	26,373	27,577
Amounts reclassified from accumulated other comprehensive income:
Net of tax	12,984	19,408	(8,495)
Other comprehensive income (loss), net of tax	(30,228)	6,965	36,072
Ending balance, net of tax	(1,395)	28,833	21,868
Foreign Currency Items [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, net of tax
Other comprehensive income (loss) before reclassifications:
Change in fair value of derivatives
Foreign currency translations	(667)
Income tax effect
Net of tax	(667)
Amounts reclassified from accumulated other comprehensive income:
Net of tax
Other comprehensive income (loss), net of tax	(667)
Ending balance, net of tax	(667)
Reclassification out of Accumulated Other Comprehensive Income [Member]
Amounts reclassified from accumulated other comprehensive income:
Operating revenue: oil/gas production	20,289
Income tax effect	(7,305)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedges [Member]
Amounts reclassified from accumulated other comprehensive income:
Operating revenue: oil/gas production	20,289	30,326	(13,274)
Income tax effect	(7,305)	(10,918)	4,779
Reclassification out of Accumulated Other Comprehensive Income [Member] | Foreign Currency Items [Member]
Amounts reclassified from accumulated other comprehensive income:
Operating revenue: oil/gas production
Income tax effect