Costs Incurred for Property Acquisition, Exploration and Development - Costs Incurred for Property Acquisition, Exploration and Development (Parenthetical) (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014
Costs Incurred Oil And Gas Property Acquisition Exploration And Development Activities [Line Items]
Costs incurred to acquire gas gathering assets	$ 407,255	[1],[2]
Gas Gathering Assets
Costs Incurred Oil And Gas Property Acquisition Exploration And Development Activities [Line Items]
Costs incurred to acquire gas gathering assets	$ 134,800

[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.