Summary of Significant Accounting Policies - Net Capitalized Costs and Associated Accumulated Depreciation, Depletion & Amortization and Non Cash Impairments (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Proved properties	$ 663,485	$ 230,800
Wells and related equipment and facilities	1,438,092	1,088,692
Support equipment and facilities	75,392	38,776
Materials and supplies	18,341	2,900
Total proved oil and gas properties	2,195,310	1,361,168
Unproved properties	328,409	18,832
Wells and facilities in progress	139,799	65,844
Total unproved oil and gas properties, excluded from amortization	468,208	84,676
Accumulated depreciation, depletion, amortization and impairment	(642,645)	(433,234)
Total oil and gas properties, net (1)	$ 2,020,873	$ 1,012,610