Costs Incurred for Property Acquisition, Exploration and Development (Detail) - USD ($) $ in Thousands		3 Months Ended	12 Months Ended
		Mar. 31, 2017	Dec. 31, 2016
Acquisitions:
Acreage purchases	[1]	$ 25,425	$ 33,142
Oil and gas properties	[1]		3,098,772
Asset retirement obligations	[1]		21,908
Development	[1]	227,177	497,795
Exploration:
Exploration drilling costs incurred	[1]	500	37,680
Gas gathering facilities:
Development	[1]	1,455	3,595
Subtotal	[1]	263,061	3,725,217
Asset retirement obligations	[1]	1,715	(24,064)
Total costs incurred	[1]	264,776	3,701,153
Expense
Exploration:
Exploration costs incurred	[1]	7,997	30,027
Stock-based compensation expense	[1]	$ 507	$ 2,298

[1] Includes costs incurred whether capitalized or expensed.