Segment Information - Amortization Expense (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Assets	$ 8,550.9	$ 9,335.8
Permian
Segment Reporting Information [Line Items]
Assets	2,188.1	2,465.7
Louisiana
Segment Reporting Information [Line Items]
Assets	2,284.8	2,562.0
Oklahoma
Segment Reporting Information [Line Items]
Assets	2,816.4	3,035.0
North Texas
Segment Reporting Information [Line Items]
Assets	1,001.7	1,135.8
Corporate
Segment Reporting Information [Line Items]
Assets	$ 259.9	$ 137.3