Acquisitions and Divestitures - Divestiture (Woodford and Mississippian Lime) (Details) $ in Thousands, MMcfe in Millions		3 Months Ended		6 Months Ended
	Jun. 04, 2015 USD ($) well term	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($) MMcfe
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Other receivable		$ 13,915		$ 13,915		$ 0
Gain on sale of oil and gas properties		21,531	$ 0	21,531	$ 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
Period the adjusted purchase price to be received within	180 days
Number of renewal terms for contract operator | term	2
Contract operator term for sold assets	1 year
Number of first spudded wells | well	14
Deferred sales proceeds	$ 1,000
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		$ 13,900