Acquisitions and Divestitures - Arkoma Divestiture - General Information (Details) - Arkoma Assets - USD ($) $ in Millions	Sep. 30, 2017	Aug. 01, 2017
Disposal Group, Disposed of by Sale, Not Discontinued Operations
Divestitures
Consideration, purchase price		$ 65.0
Contingent payments based on natural gas prices		2.5
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Scenario, Adjustment
Divestitures
Consideration, purchase price		$ 7.3
Disposal Group, Held-for-sale, Not Discontinued Operations
Divestitures
Contingent payments based on natural gas prices	$ 0.0