Asset Impairment - Summary of Impairments Recognized (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	$ 6,583	$ 1,246
Impairment of oil and gas properties held-for-sale	0	1,667
Asset impairment charges, including discontinued operations	6,583	2,913
Permian Basin and San Juan Basin [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	2,253
Permian Basin
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	2,005	1,247
San Juan Basin
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	248	(1)
North Louisiana and East Texas Natural Gas and Oil Properties
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of oil and gas properties held-for-sale	0	1,667
Oil | Permian Basin
Impaired Long-Lived Assets Held and Used [Line Items]
Asset impairment	$ 4,330	$ 0