Acquisitions and Divestitures - Arkoma Divestiture - General Information (Details) - Arkoma Assets - USD ($) $ in Millions	Aug. 01, 2017	Jun. 30, 2017
Disposal Group, Held-for-sale, Not Discontinued Operations
Divestitures
Contingent payments based on natural gas prices		$ 0.0
Other Current Liabilities | Disposal Group, Held-for-sale, Not Discontinued Operations
Divestitures
Deposit		$ 4.9
Subsequent Event | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Divestitures
Consideration, purchase price	$ 65.0
Contingent payments based on natural gas prices	$ 2.5