Quarterly Financial Data - Schedule Of Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2016		Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effect of Fourth Quarter Events [Line Items]
Estimated litigation liability, after tax	$ 37,000
Basic eps litigation settlement	$ 0.10
Diluted eps estimated litigation settlement	$ 0.10
Loss on extinguishment of debt									$ 26,055	[1]	$ 0		$ 0		$ 0		$ 554	$ 26,055	$ 0
Total revenues	$ 1,047,172	[2]	$ 726,743	[2]	$ 661,486	[2]	$ 685,427	[2]	549,689	[2]	526,199	[2]	451,211	[2]	453,174	[2]	3,120,828	1,980,273	2,680,167
Gain (loss) on derivative instruments, net	8,165	[2]	8,602	[2]	28,022	[2]	46,858	[2]	(47,382)	[2]	15,668	[2]	(82,257)	[2]	42,112	[2]	91,647	(71,859)	91,085
Property impairments	27,552	[3]	35,130	[3]	123,316	[3]	51,372	[3]	34,564	[3]	57,689	[3]	66,112	[3]	78,927	[3]	237,370	237,292	402,131
Litigation settlement	59,600	[4]	0		0		0										59,600	0	0
Gain (Loss) on Disposition of Property Plant Equipment	54,420	[5]	3,562	[5]	780	[5]	(3,638)	[5]	201,315	[5]	6,158	[5]	96,907	[5]	109	[5]	(55,124)	(304,489)	(23,149)
Income from operations	309,468		91,753		(29,041)		77,221		155,299		(93,183)		(110,547)		(239,103)		449,401	(287,534)	(224,001)
Tax benefit from US tax reform legislation																	(713,655)	0	0
Net income (loss)	$ 841,914	[6]	$ 10,621		$ (63,557)		$ 469		$ 27,670		$ (109,621)		$ (119,402)		$ (198,326)		$ 789,447	$ (399,679)	$ (353,668)
Net income per share: Basic	$ 2.27		$ 0.03		$ (0.17)		$ 0.00		$ 0.07		$ (0.30)		$ (0.32)		$ (0.54)		$ 2.13	$ (1.08)	$ (0.96)
Net income per share: Diluted	$ 2.25		$ 0.03		$ (0.17)		$ 0.00		$ 0.07		$ (0.30)		$ (0.32)		$ (0.54)		$ 2.11	$ (1.08)	$ (0.96)

[1] See Note 7. Long-Term Debt for discussion of the loss recognized by the Company upon the redemption of its 2020 Notes and 2021 Notes in the 2016 fourth quarter

[2] Gains and losses on crude oil and natural gas derivative instruments are reflected in “Total revenues” on both the consolidated statements of comprehensive income (loss) and this table of unaudited quarterly financial data. Crude oil and natural gas derivative gains and losses have been shown separately to illustrate the fluctuations in revenues that are attributable to the Company’s derivative instruments. Commodity price fluctuations each quarter can result in significant swings in mark-to-market gains and losses, which affects comparability between periods.

[3] Property impairments have been shown separately to illustrate the impact on quarterly results attributable to write downs of the Company’s assets. Commodity price fluctuations each quarter can result in significant changes in estimated future cash flows and resulting impairments, which affects comparability between periods.

[4] Fourth quarter 2017 results include a $59.6 million pre-tax loss accrual recognized in conjunction with a litigation settlement as discussed in Note 10. Commitments and Contingencies, which resulted in an after-tax decrease in net income of $37.0 million ($0.10 per basic and diluted share).

[5] Gains on asset sales have been shown separately to illustrate the impact on quarterly results attributable to asset dispositions, which differ in significance from period to period and affect comparability. See Note 14. Property Dispositions for a discussion of notable dispositions.

[6] Fourth quarter 2017 results reflect the remeasurement of the Company's deferred income tax assets and liabilities in response to the enactment of the Tax Reform Act in December 2017, which resulted in a one-time decrease in income tax expense and corresponding increase in net income of approximately $713.7 million ($1.92 per basic share and $1.91 per diluted share). See Note 8. Income Taxes for further discussion.