Costs Incurred for Property Acquisition, Exploration and Development (Detail) - USD ($) $ in Thousands		3 Months Ended			12 Months Ended
		Mar. 31, 2016		Mar. 31, 2015	Dec. 31, 2015
Costs Incurred Oil And Gas Property Acquisition Exploration And Development Activities [Line Items]
Acreage purchases	[1]	$ 5,341			$ 73,025
Development	[1]	120,903			708,268
Exploration:
Exploration drilling costs incurred	[1]	9,097			87,505
Stock-based compensation expense		12,907		$ 14,491
Gas gathering facilities:
Development	[1]	848			13,337
Subtotal	[1]	141,102			903,541
Asset retirement obligations		1,015	[1]	15,813	22,184	[1]
Total costs incurred	[1]	142,117			925,725
Expense
Exploration:
Exploration costs incurred	[1]	4,223			18,421
Stock-based compensation expense		$ 690	[1]	$ 732	$ 2,985	[1]

[1] Includes costs incurred whether capitalized or expensed.