Costs Incurred for Property Acquisition, Exploration and Development (Detail) - USD ($) $ in Thousands		6 Months Ended			12 Months Ended
		Jun. 30, 2021		Jun. 30, 2020	Dec. 31, 2020
Acquisitions:
Acreage purchases	[1]	$ 10,142			$ 26,166
Development	[1]	207,354			369,093
Gas gathering facilities:
Development	[1]	2,179			3,694
Subtotal	[1]	235,673			439,317
Asset retirement obligations		2,098	[1]	$ 4,247	2,610	[1]
Total costs incurred	[1]	237,771			441,927
Exploration Expense
Exploration:
Drilling	[1]	5,432			7,709
Expense	[1]	9,818			31,376
Stock-based compensation expense	[1]	$ 748			$ 1,279

[1] Includes costs incurred whether capitalized or expensed.