Segment Information - Assets (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Segment Reporting
Total identifiable assets	$ 8,516.3	$ 8,550.9
Permian
Segment Reporting
Total identifiable assets	2,292.8	2,236.3
Louisiana
Segment Reporting
Total identifiable assets	2,316.7	2,312.4
Oklahoma
Segment Reporting
Total identifiable assets	2,743.8	2,847.6
North Texas
Segment Reporting
Total identifiable assets	986.0	1,008.6
Corporate
Segment Reporting
Total identifiable assets	$ 177.0	$ 146.0