Acquisition and Disposition of Properties - Held for Sale (Details) (USD $) In Millions, unless otherwise specified		3 Months Ended
	Dec. 31, 2013 Natural Gas Basis - San Juan MBoe	Sep. 30, 2014 Discontinued Operations, Held-for-sale or Disposed of by Sale Natural Gas Basis - Permian	Sep. 30, 2014 Discontinued Operations, Held-for-sale or Disposed of by Sale Natural Gas Basis - San Juan
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Non-cash impairment writedown		$ 31.2	$ 147.9
Proved Developed Reserves (Energy)	73,070