Costs Incurred for Property Acquisition, Exploration and Development (Detail) - USD ($) $ in Thousands		9 Months Ended			12 Months Ended
		Sep. 30, 2020		Sep. 30, 2019	Dec. 31, 2019
Acquisitions:
Acreage purchases	[1]	$ 11,864			$ 57,324
Development	[1]	283,354			666,984
Gas gathering facilities:
Development	[1]	2,764			3,583
Subtotal	[1]	321,173			764,574
Asset retirement obligations		4,587	[1]	$ 812	11,193	[1]
Total costs incurred	[1]	325,760			775,767
Expense
Exploration:
Exploration costs incurred	[1]	22,296			35,117
Stock-based compensation expense	[1]	$ 895			$ 1,566

[1] Includes costs incurred whether capitalized or expensed.