Summary of Property and Equipment (Detail) $ in Thousands	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2021 USD ($) $ / bbl	Sep. 30, 2020 USD ($) $ / bbl	Jun. 30, 2021 USD ($)	Sep. 30, 2021 USD ($) $ / bbl	Sep. 30, 2020 USD ($) $ / bbl	Dec. 31, 2020 USD ($)
Property, Plant and Equipment [Abstract]
Proved Oil and Gas Property, Full Cost Method	$ 1,762,268			$ 1,762,268		$ 1,545,910
Unproved Oil and Gas Property, Full Cost Method	59,560			59,560		49,935
Oil and Gas Property, Full Cost Method, Gross	1,821,828			1,821,828		1,595,845
Total properties and equipment	1,850,093			1,850,093		1,623,591
Other property and equipment	28,265			28,265		27,746
Accumulated depreciation, depletion, amortization and impairments	(985,215)			(985,215)		(900,042)
Property and equipment, net (successful efforts method)	864,878			864,878		723,549
Unproved Oil and Gas Property excluded	59,600			59,600		$ 49,900
Capitalized Costs of Unproved Properties Excluded from Amortization, Period Cost			$ 1,200
Undeveloped Leasehold Costs Transferred				13,800	$ 4,500
Capitalized Costs, Proved Properties	$ 2,800	$ 1,300		2,800	1,300
Interest Costs Capitalized				$ 2,600	$ 2,100
Amortization Expense Per Physical Unit of Production | $ / bbl	12.96	16.63		12.96	16.63
Impairments of oil and gas properties	$ 0	$ 235,989		$ 1,811	$ 271,498