Costs Incurred for Property Acquisition, Exploration and Development - Costs Incurred for Property Acquisition, Exploration and Development (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended			12 Months Ended
	Mar. 31, 2014		Mar. 31, 2013	Dec. 31, 2013
Costs Incurred Oil And Gas Property Acquisition Exploration And Development Activities [Line Items]
Acreage purchases	$ 48,597	[1]		$ 137,538	[1]
Development	223,912	[1]		938,668	[1]
Gas gathering facilities:
Development	3,618	[1]		47,086	[1]
Subtotal	298,711	[1]		1,377,443	[1]
Asset retirement obligations	3,218	[1]	1,690	76,373	[1]
Total costs incurred	301,929	[1]		1,453,816	[1]
Drilling
Exploration:
Exploration costs incurred	7,737	[1]		189,742	[1]
Expense
Exploration:
Exploration costs incurred	13,694	[1]		60,384	[1]
Stock-based compensation expense
Exploration:
Exploration costs incurred	$ 1,153	[1]		$ 4,025	[1]

[1] Includes cost incurred whether capitalized or expensed.