Accumulated Other Comprehensive Income (Loss) - Schedule of Changes in Accumulated Other Comprehensive Income Loss (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance, net of tax			$ (39,789)
Amounts reclassified from accumulated other comprehensive income:
Ending balance, net of tax	$ (519,661)		(519,661)
Cash Flow Hedges
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance, net of tax	7,400	$ 46,500	24,000	$ 86,800
Other comprehensive income (loss) before reclassifications:
Change in fair value of derivatives	2,300	31,600	(1,700)	35,700
Foreign currency translations		0		0
Income tax effect	(800)	(11,500)	600	(12,800)
Net of tax	1,500	20,100	(1,100)	22,900
Amounts reclassified from accumulated other comprehensive income:
Income tax effect	(2,700)	(14,400)	(10,400)	(38,500)
Net of tax	5,000	25,500	19,000	68,600
Other comprehensive loss, net of tax	(3,500)	(5,400)	(20,100)	(45,700)
Ending balance, net of tax	3,900	41,100	3,900	41,100
Cash Flow Hedges | Operating revenue: oil/natural gas production
Amounts reclassified from accumulated other comprehensive income:
Operating revenue: oil/natural gas production	7,700	39,900	29,400	107,100
Cash Flow Hedges | Other operational expenses
Amounts reclassified from accumulated other comprehensive income:
Operating revenue: oil/natural gas production			0
Foreign Currency Items
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance, net of tax		(5,800)	(6,000)	(3,500)
Other comprehensive income (loss) before reclassifications:
Change in fair value of derivatives		0	0	0
Foreign currency translations		(200)		(2,500)
Income tax effect		0	0	0
Net of tax		(200)	0	(2,500)
Amounts reclassified from accumulated other comprehensive income:
Income tax effect		0	0	0
Net of tax		0	(6,000)	0
Other comprehensive loss, net of tax		(200)	6,000	(2,500)
Ending balance, net of tax	0	(6,000)	0	(6,000)
Foreign Currency Items | Operating revenue: oil/natural gas production
Amounts reclassified from accumulated other comprehensive income:
Operating revenue: oil/natural gas production		0	0	0
Foreign Currency Items | Other operational expenses
Amounts reclassified from accumulated other comprehensive income:
Operating revenue: oil/natural gas production			(6,000)
AOCI Attributable to Parent
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance, net of tax		40,700	18,000	83,300
Other comprehensive income (loss) before reclassifications:
Change in fair value of derivatives		31,600	(1,700)	35,700
Foreign currency translations		(200)		(2,500)
Income tax effect		(11,500)	600	(12,800)
Net of tax		19,900	(1,100)	20,400
Amounts reclassified from accumulated other comprehensive income:
Income tax effect		(14,400)	(10,400)	(38,500)
Net of tax		25,500	13,000	68,600
Other comprehensive loss, net of tax		(5,600)	(14,100)	(48,200)
Ending balance, net of tax	$ 3,900	35,100	3,900	35,100
AOCI Attributable to Parent | Operating revenue: oil/natural gas production
Amounts reclassified from accumulated other comprehensive income:
Operating revenue: oil/natural gas production		$ 39,900	29,400	$ 107,100
AOCI Attributable to Parent | Other operational expenses
Amounts reclassified from accumulated other comprehensive income:
Operating revenue: oil/natural gas production			$ (6,000)