Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
Balance Sheet Grouping, Financial Statement Captions
Carrying Value	$ 566.1	$ 575.2
Fair Value | Senior Notes
Balance Sheet Grouping, Financial Statement Captions
Fair Value	159.5	155.7
Fair Value | Ark 2007 Notes
Balance Sheet Grouping, Financial Statement Captions
Fair Value	29.2	28.4
Fair Value | Ark 2021 Notes
Balance Sheet Grouping, Financial Statement Captions
Fair Value	166.1	163.1
Fair Value | Kudu Credit Facility
Balance Sheet Grouping, Financial Statement Captions
Fair Value	224.9	223.9
Fair Value | Other Operations debt
Balance Sheet Grouping, Financial Statement Captions
Fair Value	33.0	38.2
Carrying Value | Senior Notes
Balance Sheet Grouping, Financial Statement Captions
Carrying Value	146.7	146.5
Carrying Value | Ark 2007 Notes
Balance Sheet Grouping, Financial Statement Captions
Carrying Value	30.0	30.0
Carrying Value | Ark 2021 Notes
Balance Sheet Grouping, Financial Statement Captions
Carrying Value	155.1	153.7
Carrying Value | Kudu Credit Facility
Balance Sheet Grouping, Financial Statement Captions
Carrying Value	203.7	208.3
Carrying Value | Other Operations debt
Balance Sheet Grouping, Financial Statement Captions
Carrying Value	$ 30.6	$ 36.7