Basis of Presentation and Significant Accounting Policies Proved Property Impairment (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of proved oil and gas properties	$ 1,700,000	$ 603,000	$ 4,914,870	$ 2,303,749	$ 828,317
Impairment of Long-Lived Assets to be Disposed of					37,000
Granite Wash formation [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of proved oil and gas properties					791,000
Rockies region
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of proved oil and gas properties			1,758,939	585,705	0
Hugoton Basin region
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of proved oil and gas properties			1,667,768	0	0
California region
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of proved oil and gas properties			537,511	22	0
TexLa region
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of proved oil and gas properties			430,859	4,836	0
Mid-Continent region
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of proved oil and gas properties			405,370	244,413	828,317
Permian Basin region
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of proved oil and gas properties			71,990	1,337,444	0
South Texas region
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of proved oil and gas properties			$ 42,433	$ 131,329	$ 0