Summary of Property and Equipment (Detail) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2021 USD ($) $ / bbl	Mar. 31, 2021 USD ($)	Jun. 30, 2020 USD ($) $ / bbl	Jun. 30, 2021 USD ($) $ / bbl	Jun. 30, 2020 USD ($) $ / bbl	Dec. 31, 2020 USD ($)
Property, Plant and Equipment [Abstract]
Proved Oil and Gas Property, Full Cost Method	$ 1,701,353			$ 1,701,353		$ 1,545,910
Unproved Oil and Gas Property, Full Cost Method	58,525			58,525		49,935
Oil and Gas Property, Full Cost Method, Gross	1,759,878			1,759,878		1,595,845
Total properties and equipment	1,788,063			1,788,063		1,623,591
Other property and equipment	28,185			28,185		27,746
Accumulated depreciation, depletion, amortization and impairments	(954,340)			(954,340)		(900,042)
Property and equipment, net (successful efforts method)	833,723			833,723		723,549
Unproved Oil and Gas Property excluded	58,500			58,500		$ 49,900
Capitalized Costs of Unproved Properties Excluded from Amortization, Period Cost		$ 1,200
Undeveloped Leasehold Costs Transferred				13,500	$ 4,400
Capitalized Costs, Proved Properties	$ 1,700		$ 1,200	1,700	1,200
Interest Costs Capitalized				$ 1,600	$ 1,400
Amortization Expense Per Physical Unit of Production | $ / bbl	12.82		16.66	12.82	16.66
Impairments of oil and gas properties	$ 0		$ 35,509	$ 1,811	$ 35,509