Costs Incurred for Property Acquisition, Exploration and Development (Detail) - USD ($) $ in Thousands		9 Months Ended			12 Months Ended
		Sep. 30, 2019		Sep. 30, 2018	Dec. 31, 2018
Acquisitions:
Acreage purchases	[1]	$ 31,582			$ 62,390
Oil and gas properties	[1]				1,683
Development	[1]	541,455			834,552
Exploration:
Exploration drilling costs incurred	[1]				1,380
Gas gathering facilities:
Development	[1]	3,127			10,218
Subtotal	[1]	603,497			944,340
Asset retirement obligations		812	[1]	$ 20,452	28,826	[1]
Total costs incurred	[1]	604,309			973,166
Expense
Exploration:
Exploration costs incurred	[1]	25,961			32,196
Stock-based compensation expense	[1]	$ 1,372			$ 1,921

[1] Includes costs incurred whether capitalized or expensed.