Segment Information - Assets (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Segment Reporting
Total identifiable assets	$ 8,667.2	$ 9,335.8
Permian
Segment Reporting
Total identifiable assets	2,245.3	2,465.7
North Texas
Segment Reporting
Total identifiable assets	1,031.2	1,135.8
Oklahoma
Segment Reporting
Total identifiable assets	2,889.1	3,035.0
Louisiana
Segment Reporting
Total identifiable assets	2,278.9	2,562.0
Corporate
Segment Reporting
Total identifiable assets	$ 222.7	$ 137.3