Supplemental Information on Oil and Gas Producing Activities (Unaudited) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Capitalized Costs Relating to Oil and Gas Producing Activities
Proved properties	$ 12,705,672	$ 11,096,462
Unproved properties	1,767,600	2,266,673
Total	14,473,272	13,363,135
Accumulated depletion and depreciation	(3,615,680)	(2,783,832)
Net capitalized costs	10,857,592	10,579,303
Costs Incurred in Certain Oil and Gas Activities
Proved property		175,650	$ 134,113
Unproved property	172,387	204,272	611,631
Development costs	1,164,800	897,287	1,000,903
Exploration costs	323,773	384,698	326,856
Total costs incurred	1,660,960	1,661,907	2,073,503
Results of Operations for Oil and Gas Producing Activities
Revenues	3,652,894	2,747,920	1,755,061
Operating expenses:
Production expenses	1,601,985	1,279,217	999,516
Exploration expenses	4,958	8,538	6,862
Depletion and depreciation	832,326	694,332	700,274
Impairment of unproved properties	549,437	159,598	162,935
Results of operations before income tax expense (benefit)	664,188	606,235	(114,526)
Income tax expense	(156,350)	(228,096)	43,334
Results of operations	$ 507,838	$ 378,139	$ (71,192)