Schedule of Changes In Accumulated Other Comprehensive Income Loss (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Jun. 18, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, net of tax	$ 24,500,000		$ 28,833,000
Other comprehensive income (loss) before reclassifications:
Change in fair value of derivatives	(30,800,000)		(20,900,000)
Foreign currency translations	300,000		(200,000)
Income tax effect	11,100,000		7,600,000
Net of tax	(19,400,000)		(13,500,000)
Amounts reclassified from accumulated other comprehensive income:
Net of tax	1,300,000		(8,900,000)
Other comprehensive income (loss), net of tax	(18,100,000)		(22,400,000)
Ending balance, net of tax	6,413,000		6,413,000
Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, net of tax	25,000,000		28,833,000	21,900,000	63,000,000
Other comprehensive income (loss) before reclassifications:
Change in fair value of derivatives	(30,800,000)	(41,800,000)	(20,900,000)	30,800,000
Income tax effect	11,100,000	15,000,000	7,600,000	(11,100,000)
Net of tax	(19,700,000)	(26,800,000)	(13,300,000)	19,700,000
Amounts reclassified from accumulated other comprehensive income:
Net of tax	1,300,000	(6,400,000)	(8,900,000)	(11,800,000)
Other comprehensive income (loss), net of tax	(18,400,000)	(33,200,000)	(22,200,000)	7,900,000
Ending balance, net of tax	6,600,000	29,800,000	6,600,000	29,800,000	63,000,000
Foreign Currency Items [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance, net of tax	(500,000)
Other comprehensive income (loss) before reclassifications:
Foreign currency translations	300,000		(200,000)
Net of tax	300,000		(200,000)
Amounts reclassified from accumulated other comprehensive income:
Other comprehensive income (loss), net of tax	300,000		(200,000)
Ending balance, net of tax	200,000		200,000
Reclassification out of Accumulated Other Comprehensive Income [Member]
Amounts reclassified from accumulated other comprehensive income:
Operating revenue: oil/gas production	2,100,000		(13,800,000)
Income tax effect	(800,000)		4,900,000
Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedges [Member]
Amounts reclassified from accumulated other comprehensive income:
Operating revenue: oil/gas production	2,100,000	(10,000,000)	(13,800,000)	(18,400,000)
Income tax effect	(800,000)	3,600,000	4,900,000	6,600,000
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