Costs Incurred for Property Acquisition, Exploration and Development (Detail) - USD ($) $ in Thousands		3 Months Ended			12 Months Ended
		Mar. 31, 2021		Mar. 31, 2020	Dec. 31, 2020
Acquisitions:
Acreage purchases	[1]	$ 6,424			$ 26,166
Development	[1]	92,654			369,093
Gas gathering facilities:
Development	[1]	1,551			3,694
Subtotal	[1]	110,598			439,317
Increase in asset retirement costs capitalized		761	[1]	$ 1,250	2,610	[1]
Total costs incurred	[1]	111,359			441,927
Exploration Expense
Exploration:
Drilling	[1]	4,431			7,709
Expense	[1]	5,151			31,376
Stock-based compensation expense	[1]	$ 387			$ 1,279

[1] Includes costs incurred whether capitalized or expensed.