Basis of Presentation and Significant Accounting Policies Unproved Property Impairment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment Of Unproved Oil And Gas Properties	$ 899,084	$ 0	$ 0
TexLa region
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment Of Unproved Oil And Gas Properties	416,846
Permian Basin region
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment Of Unproved Oil And Gas Properties	226,922
Rockies region
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment Of Unproved Oil And Gas Properties	184,137
California region
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment Of Unproved Oil And Gas Properties	$ 71,179