Summary of Significant Accounting Policies - Net Capitalized Costs and Associated Accumulated Depreciation, Depletion & Amortization and Non Cash Impairments (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Proved properties	$ 667,346	$ 663,485
Wells and related equipment and facilities	1,518,824	1,438,092
Support equipment and facilities	88,901	75,392
Materials and supplies	21,600	18,341
Total proved oil and gas properties	2,296,671	2,195,310
Unproved properties	328,377	328,409
Wells and facilities in progress	162,491	139,799
Total unproved oil and gas properties, excluded from amortization	490,868	468,208
Accumulated depreciation, depletion, amortization and impairment	(714,237)	(642,645)
Total oil and gas properties, net	$ 2,073,302	$ 2,020,873