Summary of Significant Accounting Policies - Net Capitalized Costs and Associated Accumulated Depreciation, Depletion & Amortization and Non Cash Impairments (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Proved properties	$ 670,270	$ 663,485
Wells and related equipment and facilities	1,647,456	1,438,092
Support equipment and facilities	90,690	75,392
Materials and supplies	24,480	18,341
Total proved oil and gas properties	2,432,896	2,195,310
Unproved properties	321,206	328,409
Wells and facilities in progress	147,679	139,799
Total unproved oil and gas properties, excluded from amortization	468,885	468,208
Accumulated depreciation, depletion, amortization and impairment	(785,345)	(642,645)
Total oil and gas properties, net	$ 2,116,436	$ 2,020,873