Impairment of Natural Gas and Crude Oil Properties (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Impairment of natural gas and crude oil properties [Line Items]
Delaware Basin Unproved Property Impairment	$ 251,600,000
Impairment of proved ad unproved properties	252,623,000	$ 338,000	$ 282,188,000	$ 2,391,000
Amortization of Individually Insignificant Unproved Properties	117,000	595,000	311,000	681,000
Impairment of Oil and Gas Properties	252,740,000	933,000	282,499,000	3,072,000
Land and buildings	0	0	0	3,032,000
Impairment of properties and equipment	252,740,000	$ 933,000	$ 282,499,000	$ 6,104,000
Impairment of other properties	$ 13,400