Costs Incurred for Property Acquisition, Exploration and Development (Detail) - USD ($) $ in Thousands		9 Months Ended			12 Months Ended
		Sep. 30, 2016		Sep. 30, 2015	Dec. 31, 2015
Acquisitions:
Acreage purchases	[1]	$ 16,282			$ 73,025
Oil and gas properties	[1]	3,086,635
Asset retirement obligations	[1]	16,609
Development	[1]	302,518			708,268
Exploration:
Exploration drilling costs incurred	[1]	37,528			87,505
Gas gathering facilities:
Development	[1]	1,345			13,337
Subtotal	[1]	3,479,558			903,541
Asset retirement obligations		4,655	[1]	$ 19,862	22,184	[1]
Total costs incurred	[1]	3,484,213			925,725
Expense
Exploration:
Exploration costs incurred	[1]	16,972			18,421
Stock-based compensation expense	[1]	$ 1,669			$ 2,985

[1] Includes costs incurred whether capitalized or expensed.