Supplemental Information on Natural Gas and Oil Exploration, Development and Production Activities (Unaudited) - Costs Incurred for Property Acquisition, Exploration and Development (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Costs Incurred Oil And Gas Property Acquisition Exploration And Development Activities [Line Items]
Acquisitions	[1],[2]	$ 0	$ 404,252	$ 0
Acreage purchases	[1]	73,025	226,475	137,538
Development	[1]	708,268	1,119,896	938,668
Exploration:
Exploration drilling costs incurred	[1]	87,505	180,925	189,742
Stock-based compensation expense		57,801	70,681	64,369
Gas gathering facilities:
Development	[1]	13,337	13,137	47,086
Subtotal	[1]	903,541	2,008,233	1,377,443
Asset retirement obligations	[1]	22,184	56,822	76,373
Total costs incurred	[1]	925,725	2,065,055	1,453,816
Expense
Exploration:
Exploration costs incurred	[1]	18,421	58,979	60,384
Stock-based compensation expense	[1]	$ 2,985	$ 4,569	$ 4,025

[1] Includes cost incurred whether capitalized or expensed.

[2] See also Note 3 for additional information related to the 2014 Conger Exchange which includes $134.8 million of gas gathering assets received in the exchange and $11.9 million of asset retirement obligations added in the exchange.