Supplemental Information on Natural Gas and Oil Exploration, Development and Production Activities (Unaudited) - Costs Incurred for Property Acquisition, Exploration and Development (Parenthetical) (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]
Acquisition Costs, Period Cost	[1],[2]	$ 0	$ 404,252	$ 0
Asset retirement obligations	[1]	$ 22,184	56,822	$ 76,373
Conger Exchange Transaction
Costs Incurred Oil And Gas Property Acquisition Exploration And Development Activities [Line Items]
Asset retirement obligations			11,900
Gas Gathering Assets
Costs Incurred Oil And Gas Property Acquisition Exploration And Development Activities [Line Items]
Acquisition Costs, Period Cost			$ 134,800

[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.