Acquisitions and Dispositions Acquisitions and Dispositions (Details) - USD ($) $ in Millions	Jul. 31, 2017	Sep. 30, 2016	Apr. 25, 2016	Apr. 15, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from Sale of Oil and Gas Property and Equipment				$ 46.9
South Bearhead Creek and Burr Ferry Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Participation Interest Sold in Oil and Gas Properties				75.00%
Proceeds from Sale of Oil and Gas Property and Equipment				$ 46.9
Buyer's Assumption of ARO				$ 6.5
Masters Creek Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from Sale of Oil and Gas Property and Equipment			$ 0.1
Buyer's Assumption of ARO			$ 8.1
Sun TSH Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from Sale of Oil and Gas Property and Equipment		$ 0.9
Buyer's Assumption of ARO		$ 1.8
AWP Olmos Wheeler Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from Sale of Oil and Gas Property and Equipment	$ 0.7
Buyer's Assumption of ARO	$ 0.5