Acquisitions and Dispositions (Details) $ in Millions	Mar. 15, 2016 USD ($)	Feb. 02, 2016 USD ($)	Dec. 31, 2015 USD ($)	Jul. 15, 2014 USD ($) a
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Texegy PSA deposit			$ 2.4
Fasken Field [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Acreage sold in oil and gas properties | a				8,300
Participation interest sold in oil and gas properties				36.00%
Sale proceeds from disposal of properties				$ 175.0
Cash Received at Closing from Oil and Gas Properties				125.0
Cash Carry of Field Development Costs				50.0
Remaining Cash Carry of Field Development Costs			5.5
Sale Proceeds Received at Closing				147.0
Deferred Credits and Other Liabilities, Current				$ 12.5
South Bearhead Creek and Burr Ferry Field [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sale proceeds from disposal of properties			$ 49.0
Interest Sold in Oil and Gas Properties			75.00%
Discontinued Operations, percentage of company reserves sold			5.00%
Remaining interest in oil and gas properties			25.00%
Subsequent Event [Member] | South Bearhead Creek and Burr Ferry Field [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sale Proceeds Received at Closing	$ 13.0
Texegy PSA deposit		$ 4.9