Acquisitions and Divestitures - Divestiture (Woodford and Mississippian Lime) (Details) $ in Thousands, MMcfe in Millions		3 Months Ended			9 Months Ended
	Jun. 04, 2015 USD ($) term	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Dec. 31, 2014 MMcfe
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale of oil and gas properties		$ 828	$ 21,500	$ 0	$ 22,359	$ 0
Woodford and Mississippian Lime
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net proceeds from sale of a majority of interests	$ 280,000
Cash received from sale	$ 257,700
Number of renewal terms for contract operator | term	2
Contract operator term for sold assets	1 year
Proved reserves | MMcfe							227
Estimated proved reserves attributable to Sold Assets (percent of total)							57.00%
Current Assets | Woodford and Mississippian Lime
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Other receivable	$ 13,900