Costs Incurred for Property Acquisition, Exploration and Development - Costs Incurred for Property Acquisition, Exploration and Development (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2014		Dec. 31, 2013
Costs Incurred Oil And Gas Property Acquisition Exploration And Development Activities [Line Items]
Acquisitions	$ 409,331	[1],[2]
Acreage purchases	143,850	[1]	137,538	[1]
Development	775,570	[1]	938,668	[1]
Gas gathering facilities:
Development	12,986	[1]	47,086	[1]
Subtotal	1,496,589	[1]	1,377,443	[1]
Asset retirement obligations	7,815	[1]	76,373	[1]
Total costs incurred	1,504,404	[1]	1,453,816	[1]
Drilling
Exploration:
Exploration costs incurred	114,942	[1]	189,742	[1]
Expense
Exploration:
Exploration costs incurred	36,502	[1]	60,384	[1]
Stock-based compensation expense
Exploration:
Exploration costs incurred	$ 3,408	[1]	$ 4,025	[1]

[1] Includes costs incurred whether capitalized or expensed.

[2] See also Note 4 for additional information related to the Conger Exchange. Includes $134.8 million of gas gathering assets.