Costs Incurred for Property Acquisition, Exploration and Development - Costs Incurred for Property Acquisition, Exploration and Development (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended		12 Months Ended
	Jun. 30, 2014		Dec. 31, 2013
Costs Incurred Oil And Gas Property Acquisition Exploration And Development Activities [Line Items]
Acquisitions	$ 407,255	[1],[2]
Acreage purchases	107,379	[1]	137,538	[1]
Development	512,703	[1]	938,668	[1]
Gas gathering facilities:
Development	7,371	[1]	47,086	[1]
Subtotal	1,100,436	[1]	1,377,443	[1]
Asset retirement obligations	5,516	[1]	76,373	[1]
Total costs incurred	1,105,952	[1]	1,453,816	[1]
Drilling
Exploration:
Exploration costs incurred	37,261	[1]	189,742	[1]
Expense
Exploration:
Exploration costs incurred	26,092	[1]	60,384	[1]
Stock-based compensation expense
Exploration:
Exploration costs incurred	$ 2,375	[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.