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Fair Value of Financial Instruments (Details) - USD ($) $ in Millions | Dec. 31, 2021 | Dec. 31, 2020
--- | --- | ---
Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Debt | $ 693.0 | $ 376.4
Fair value | Ark 2007 Notes |  |
Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Debt, fair value | 27.6 | 0.0
Fair value | Ark 2021 Notes |  |
Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Debt, fair value | 162.8 | 0.0
Fair value | NSM Bank Facility |  |
Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Debt, fair value | 275.8 | 279.3
Fair value | Other NSM |  |
Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Debt, fair value | 1.0 | 1.3
Fair value | Kudu Credit Facility |  |
Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Debt, fair value | 246.8 | 0.0
Fair value | Kudu Bank Facility |  |
Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Debt, fair value | 0.0 | 89.3
Fair value | Other Operations |  |
Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Debt, fair value | 17.7 | 18.8
Carrying Value | Ark 2007 Notes |  |
Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Debt | 30.0 | 0.0
Carrying Value | Ark 2021 Notes |  |
Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Debt | 155.9 | 0.0
Carrying Value | NSM Bank Facility |  |
Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Debt | 271.2 | 271.3
Carrying Value | Other NSM |  |
Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Debt | 0.9 | 1.3
Carrying Value | Kudu Credit Facility |  |
Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Debt | 218.2 | 0.0
Carrying Value | Kudu Bank Facility |  |
Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Debt | 0.0 | 86.3
Carrying Value | Other Operations |  |
Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Debt | $ 16.8 | $ 17.5

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