Summary of Significant Accounting Policies - Net Capitalized Costs and Associated Accumulated Depreciation, Depletion & Amortization and Non Cash Impairments (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Proved properties	$ 720,735	$ 725,964
Wells and related equipment and facilities	1,919,297	1,805,136
Support equipment and facilities	105,965	99,540
Materials and supplies	12,487	13,489
Total proved oil and gas properties	2,758,484	2,644,129
Unproved properties	179,492	265,387
Wells and facilities in progress	52,391	92,406
Total unproved oil and gas properties, excluded from amortization	231,883	357,793
Accumulated depreciation, depletion, amortization and impairment	(2,248,522)	(958,475)
Total oil and gas properties, net	$ 741,845	$ 2,043,447